Chem 201 Lecture Notes Sem I 2017-2018
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Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 TOPI C1: I NTRODUCTI ONANDREVI EW 1. 1TheOr i gi nandDef i ni t i onofOr gani cChemi st r y t h 18 cent ur y( neart heend) :Compounds/ mat er i al swer econsi der edor gani c( i fobt ai nedf r om nat ur alorl i v i ngsour ces/ or gani sms)ori nor gani c( i fobt ai nedf r om nonl i v i ngsour ces– mi ner al sandt hel i ke) . Ear l y19thcent ur y :JonsJacobBer zel i uscoi nedt het er m“ or gani cchemi st r y ”f ort hest udyof compoundsder i v ed f r om nat ur alsour ces.Thi swasaf undament aldi f f er encebet ween or gani candi nor gani cmat er i al s. Lat er ,Fr i edr i chWohl er ,aGer manobser v edat r ansf or mat i onofani nor gani ccompound ( ammoni um cy anat e)t oanor gani ccompound( ur ea)whi chsett hepacef ort heov er t ur ni ng +oft hedogmaofv i t al i sm: NH4 OCN O=C( NH2) 2 Ammoni uncy anat e Ur ea Mor et hant wodecadesofi nt enser esear chbyt heGer manchemi stHer mannKol beand Engl i shchemi st , Edwar dFr ankl and, i npar t i cul ar , l eadi ngt ot hesy nt hesi sofacet i caci df r om ani nor gani csour ce, deal taf i nal bl owt ot het heor yofv i t al i sm. I twasest abl i shedf r om combust i onanal y si st hator gani ccompoundscont ai nedcar bon; t hus,t hi sdef i ni t i onofor gani cchemi st r yemer ged:or gani cchemi st r yi st hest udyofcar bon compounds. 1. 2Sour cesandabundanceofor gani ccompounds Pl ant sandani mal s( conv eni entsour ces) . Pet r ol eum andcoal( bot hf r om decay edpl ant sandani mal s)ar et wol ar ger eser v oi r sof or gani cmat er i al s. Theabundanceofcar boncompoundsi sduet o:( i )t heabi l i t yofcar bonat omst ol i nkwi t h eachot hert of or m chai nsandr i ngs,aphenomenonr ef er r edt oascat enat i on;( i i )t heabi l i t y ofcar bont of or m mul t i pl ebondst oi t sel fandot herel ement s( chi ef l yhy dr ogen,butal so oxy gen, sul f ur , ni t r ogen, phosphor usandt hehal ogen) . 1. 3TheSt r uct ur al Theor y Pr oposedi ndependent l ybyAugustKekul e, Ar chi bal dS.Cooper , andAl exanderM.But l er ov . Or i gi nat es f r om t he conceptofi somer i sm and i s based on t he i dea t hata pr eci se ar r angementofat omsuni quel ydef i nesasubst ance. I thast o do wi t ht heel ect r onst hathol dt hem t oget her ,t heshapesand si zesoft he mol ecul est hatt heseat omsf or m, andwi t ht hewayt hatel ect r onsar edi st r i but edov ert hem. 1. 4Chemi cal Bondi ngandMol ecul arSt r uct ur e Thest r uct ur esofor gani cmol ecul esdependont heat omst heycont ai nandt hewayt hese 1 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 at omsar econnect ed. 1. 4. 1At oms, El ect r onsandOr bi t al s Theat om i scomposedofel ement ar ypar t i cl escal l edpr ot ons,neut r onsandel ect r ons. Pr ot ons ( posi t i v el y char ged)and neut r ons ( el ect r i cal l y neut r al )r esi de i nt he nucl eus sur r oundedbyacl oudofor bi t i ngel ect r ons. Anat om i sdescr i bedbyi t sat omi cnumber( Z) ,whi chgi v est het ot alnumberofpr ot onsi n t henucl eus, andt hemassnumber( A)whi chgi v est het ot alnumberofpr ot onsandneut r ons i nt henucl eus.I naneut r al at om, #ofpr ot onsequal s#ofel ect r ons. El ect r onswer econsi der edaspar t i cl esunt i li n1924whent heFr enchphy si ci stLoui sde Br ogl i esuggest edt hatt heyhav ewav el i kepr oper t i es. Lat eri n1926, Er wi nSchr odi ngercal cul at edt heener gyofanel ect r oni nahy dr ogenat om by usi ngequat i onst hatt r eat edt heel ect r onasi fi twer eawav e.I nst eadofasi ngl eener gy , Schr odi ngerobt ai ned a ser i es of ener gy l ev el s,each cor r espondi ng t o a di f f er ent mat hemat i caldescr i pt i onoft heel ect r onwav e.Eachdescr i pt i oni scal l edawav ef unct i on, denot edaspsi ( ψ) . ThenHei senber gpr oposedt hatwecannotexact l yt el lwher eanel ect r oni s,butwecant el l i t spr obabl el ocat i on.Thepr obabi l i t yofl ocat i nganel ect r onatapar t i cul arspotr el at i v et oan at om’ snucl eusi sgi v enasψ2.Gr eat ert hedi st anceawayf r om t henucl eus,l essert he pr obabi l i t y , butψ2≠0.Awav ef unct i oni scal l edanor bi t al . Or bi t al sar edescr i bedbyspeci f y i ngt hei rsi z e, shape, anddi r ect i onal pr oper t i es. sor bi t al . …. spher i calshape por bi t al . …. . dumbbel l “ dor bi t al …….compl ex for bi t al……. “ “ “ Thesi zeofanor bi t ali sshownbyt hepr i nci palquant um number ,n( n=1, 2, 3,et c. )whi ch st speci f i est heener gyl ev el orshel l oft heor bi t al .Ansor bi t al i nt he1 shel l i sdenot edas1s. 2 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 1. 4. 2El ect r oni cConf i gur at i on El ect r onconf i gur at i oni st hear r angement / di st r i but i onoft heel ect r onsi nanat om. Rest r i ct i onRul es Paul i ’ sexcl usi onpr i nci pl e:onl yt woel ect r onscanoccupyt hesameor bi t al ,andt odoso t heset womusthav eopposi t espi ns. Auf baupr i nci pl e:el ect r onsofanat om occupyquant um l ev el soror bi t al sst ar t i ngf r om t he l owestener gyl ev el , andpr oceedi ngt ot hehi ghest . Hund’ sr ul e:Foror bi t al sofequalener gy ,eachi ssi ngl yoccupi edbef or eanyonei sdoubl y occupi ed. El ect r oni cconf i gur at i onsofSomeAt oms Or bi t al f i l l i ng Val enceel ect r onsar et heout er mostel ect r ons( i nt hehi ghestoccupi edener gyl ev elorshel l ) . Hence, t hi sshel l i scal l edv al enceshel l . Forexampl e, i nacar bonat om, t hehi ghestoccupi edener gyl ev elcont ai nst heseor bi t al s:2s, 2px, 2pyand2pz.Thesum ofel ect r onsi nt heseor bi t al si s4.Ther ef or e, acar bonat om has4 v al enceel ect r ons.Thenobl egases( neon,ar gon,et c. )eachhasei ght( 8)v al enceel ect r ons andar esai dt ohav eacompl et eoct etofel ect r ons.Hel i um i sal soanobl egas. 1. 4. 3Ty pesofChemi cal Bonds Theat t r act i v ef or cebet weenat omsi nacompoundi sachemi cal bond. Whenev erat omsr eactt of or m mol ecul esori ons, t heydosoi nsuchawayast oensur et hat ev er ynonhy dr ogenat om i nt hemol ecul epossessesacompl et eoct etofel ect r onsi nt he v al enceshel l .Thi si sknownast heLewi soct etr ul e. Twoki ndsofchemi cal bonds: Bondi ngbyt het r ansf erofel ect r onsf r om oneat om t oanot her 3 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 ( i oni cbondi ng)orbyt heshar i ngofapai rofel ect r ons( cov al entbondi ng) . I oni cBondi ng Acompl et et r ansf erofel ect r onl eadst ot hef or mat i onoft woopposi t el ychar gedspeci es ( i ons) .The i oni cbondi st heel ect r ost at i cat t r act i onbet weent heseopposi t el ychar ged speci es( i ons) . At om t hatl osesanel ect r on-cat i ons; at om t hatgai nst hel ostel ect r on-ani ons. Consi dert heexampl ebel ow: + Ther ef or e, l i t hi um f l uor i dei s: Li F SAMPLEPROBLEM: I l l ust r at et hebondi ngi nt hef ol l owi ngcompounds: ( a)Sodi um ni t r i de ( b)Magnesi um chl or i de Al ar geamountofener gy , cal l edt hei oni zat i onener gy , mustbeaddedt oanat om i nor dert o r emov eoneofi t sel ect r ons, t hepr ocessbei ngendot her mi c.Thel owert hei oni zat i onener gy , t heeasi eri ti st or emov et heel ect r on, t husf or mi ngt hecat i on. Theener gychangef ort headdi t i onofanel ect r ont oanat om i scal l edi t sel ect r onaf f i ni t y , t he pr ocessbei ngexot her mi c. SAMPLEPROBLEMS 1. Whi choft hef ol l owi ngi onspossessanobl egasel ect r oni cconf i gur at i on?K+, He+, H-, O-, F-, 2+ Ca . 2. Whati st heel ect r oni cconf i gur at i onofC+?ofC-?Doesei t heroneoft hesei onshav eanobl e gasconf i gur at i on? 1. 4. 3. 2Cov al entbondi ng G. N.Lewi sexpl ai nedt hef or mat i onofst abl edi at omi cmol ecul essuchasH2,F2,et c. ,bya pr ocessofshar i ngel ect r onpai r s. Exampl es: 4 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 1) H. . H H: H Twohy dr ogenat omseachwi t h Hy dr ogenmol ecul e asi ngl eel ect r on Thesear eLewi s st r uct ur es I nt heLewi sst r uct ur eofF2mol ecul e, t her ear ebot hbondi ngandnonbondi ng( l one)pai r s. Wr i t i ngLewi sdotSt r uct ur es I nwr i t i ngLewi sst r uct ur es, r emembert hat : One cannotassi gn an el ect r on i n a mol ecul e as or i gi nat i ng on anypar t i cul ar componentat om. Val enceshel lof2nd r ow el ement soft heper i odi ct abl e( Li ,Be,B,C,N,O,F)hasa maxi mum of8el ect r ons.Butt hi si sanexcept i onf ort he3rdorl owerr ows;t heydo expandt hei rout er shel l oct et swhennecessar y . Rul esf orwr i t i ngLewi sst r uct ur es Det er mi net het ot al #ofv al enceel ect r onsav ai l abl ef ort hef or mat i onofbondi ngandnonbondi ngel ect r onpai r s: ( Sum ofv al enceel ect r onsf r om eachcomponentat om)-( Char geoni on) Est abl i sht heconnect i v i t yoft heat oms( whi chat om i sbondedt owhi ch) .Not e: Hy dr ogeni s nev ert hecent r al at om; f l uor i nei sal sonev ert hecent r al at om; t hemostel ect r oposi t i v eat om ( excepthy dr ogen)i susual l y( butnotal way s!t hecent r al at om. Connectt heat omsusi ngcov al entbondssot hatev er yat om i sconnect edt oatl eastone ot herbyacov al entbond. Di st r i but et her emai ni ngel ect r ons( i fany ) . SAMPLEPROBLEMS 1. Wr i t et heLewi sst r uct ur ef or( a)hy dr ogenf l uor i de,HF( b)ammoni a,NH3 ( c)f or mal dehy de, CH2O( d)ur ea, CH4N2O 2. Wr i t esat i sf act or yLewi sst r uct ur esf or :( a)et hane,C2H6 ( b)acr y l oni t r i l e,C3H3N( c)met hy l 5 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 al cohol , CH4O( d)acet y l ene, C2H4 ( e)hy dr ogency ani de, CHN( f )t r i met hy l bor ane, C3H9B 3. Fort hemol ecul arf or mul a,HCNO,manyLewi sst r uct ur esmaybewr i t t en.Wr i t eatl eastf i v e oft hesest r uct ur es. 1. 4. 3. 3Val enceBondDescr i pt i onofCov al entBond Accor di ngt ot hev al encebondt heor y ,“ acov al entbondi sf or medbyt heov er l apoft wo si ngl yoccupi edat omi c. ” Howev er , t hev al encebondt heor yf ai l st oexpl ai nt hechemi calbondi ngi nsi mpl emol ecul es l i kemet hane, CH4. Cl ear l y ,car bonhasonl yt wosi ngl yoccupi edor bi t al s( 2pxand2py) ;t her ef or e,car bonshoul d onl yf or mt wochemi cal bonds.Howev er , car bonhast het endencyt of or m 4bonds. Mul t i pl eBonds Adoubl ebond( 2pai r sofshar edel ect r ons)consi st sofasi gmabondandapi bond. At r i pl ebond( 3pai r sofel ect r ons)consi st sofasi gmabondandt wopi bonds. 1. 4. 3. 5Hy br i di zat i onTheor yDescr i pt i onofCov al entBond Hy br i di zat i ont heor yst at est hat :“ acov al entbondi sf or medbyt heov er l apoft wosi ngl y occupi edhy br i dorat omi cor bi t al s” . Hy br i dat omi cor bi t al sar ecr eat edbymi xi ngt oget herat omi cor bi t al st of or m anequal numberofnewhy br i dat omi cor bi t al s. ”Hy br i dor bi t al sar eusual l yf or medbymi xi ngt oget her 2sand2por bi t al s. Dependi ngont henumberof2por bi t al si ncl uded,onecanf or m sp,sp2,andsp3 hy br i d or bi t al s.The#ofor bi t al scombi ned=#ofsi gmabondsandl onepai rel ect r onsonanat om. Ther esul t i nghy br i di z edor bi t al sar esepar at edf r om eachot herasmuchaspossi bl e. NB.Onl ysp, sp2, andsp3ar ei mpor t anti nor gani cchemi st r y .Eacht y peofhy br i dor bi t al i sassoci at ed wi t hapar t i cul art y peofel ect r ondomai ngeomet r y . El ect r ondomai ni sar egi oni nspace( ar oundapar t i cul arat om)t hatcont ai nsel ect r ons.I t r ef er st ot henumberofl onepai r sorbondsar oundapar t i cul arat om i namol ecul e. El ect r ondomai ngeomet r yi st hear r angementofel ect r onsar oundapar t i cul arat om. 6 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2el ect r ondomai ns l i nearshape 3el ect r ondomai ns t r i gonal pl anarshape 4el ect r ondomai ns t et r ahedr al shape Doubl eandt r i pl ebondscountasoneel ect r ondomai n. Hy br i dor bi t al set #ofel ect r on domai ns Sp 2 2 sp 3 sp3 4 sp3d 5 sp3d2 6 Bondangl es: sp=180o sp2=120o El ect r ondomai ngeomet r y Li near t r i gonal pl anar Tet r ahedr al t r i gonal bi py r ami dal Oct ahedr al sp3=109. 5o Sampl ePr obl ems/ Exer ci ses 1. Howmanyel ect r ondomai nsar econt ai nedar oundeachcent r al at om?Whati st heel ect r on domai ngeomet r y ?( a)HCN ( b)CO ( c)H2O ( c)SO2 ( d)PCl e)CH4 5( 2. I dent i f yt heel ect r ondomai ngeomet r yf orC, O, andNf ort hef ol l owi ngcompound: 3. I dent i f yt hehy br i dor bi t al susedbyeachCi nt hef ol l owi ngcompound: 4. Gi v et hehy br i di zat i onandgeomet r yofeachoft hef ol l owi ng:( a)NH3 ( b)CH3OCH3 ( c) CH3CHO 5. Gi v et hehy br i di zat i onst at eofeachcar boni nt hef ol l owi ngcompounds:( a)car bondi oxi de, O=C=O 6. Gi v et heshapesar oundal l nonhy dr ogenat omsoft hef ol l owi ngmol ecul es: ( a)CHCl 3 ( b)CH3CN ( c)( CH3) 3N 7. Foreachoft hecompoundsbel ow, gi v et henumberofsp3car bons, sp2car bons, spcar bons, CCσbonds, πbondst ocar bon: 7 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Bondangl escannotbeexpl ai nedwi t hsi mpl esandpor bi t al s.VSEPRt heor yshoul dbeused. Hy br i di zedor bi t al sar el oweri nener gybecauseel ect r onpai r sar ef ar t herapar t . 1. 4. 3. 6Char geDi st r i but i on Exceptf ordi at omi cmol ecul es,t heel ect r onpai r si ncov al entbondsar eshar edabsol ut el y ev enl y .Mostcov al entcompoundsshowsomedegr eeofl ocalchar gesepar at i on, r esul t i ngi n bondand/ ormol ecul ardi pol es.Adi pol eexi st swhent hecent er sofposi t i v eandnegat i v e char gedi st r i but i ondonotcoi nci de. For mal Char ges Al ar gel ocal char gesepar at i onusual l yr esul t swhenashar edel ect r onpai ri sdonat ed uni l at er al l y . Exampl e: I ngener al ,f orcov al ent l ybondedat omshav i ngv al enceshel lel ect r onoct et s,i ft he#of cov al entbondst oanat om >i t snor malv al ence,i twi l lcar r yaposi t i v echar ge.I ft he#of cov al entbondst oanat om <i t snor malv al ence, i twi l lcar r yanegat i v echar ge.Foraneut r al mol ecul e,sum ofi t sposi t i v echar gesequal ssum ofi t snegat i v echar ges.Theseposi t i v e char gesar ecal l edf or malchar ges. For mal char ge=Gr oup#i nper i odi ct abl e-#ofbonds-#ofunshar edel ect r ons OR, For mal char ge=Val encee-i nneut r al at om –( Unshar edv al encee-+Hal foft heshar ede-) El ect r onsi ncov al entbondsar ecount edasi ft heyar eshar edequal l ybyt heat omst hey connect , butunshar edel ect r onsbel ongt oasi ngl eat om.Thati swhyonl yhal ft henumberof el ect r onsi ncov al entbondscanbeconsi der edt obe“ owned”byanat om. Exampl e: Cal cul at et hef or mal char geoneachoft heat omsi nt heLewi sst r uct ur esbel ow: 8 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 1. 4. 3. 7Cov al entBondPol ar i t yandEl ect r onegat i v i t y Whet herornotel ect r ont r ansf erorshar i ngwi l loccurdependsupont heel ect r onegat i v i t y di f f er encebet weent het woat oms.El ect r onegat i v i t yi st het endencyofanat om t odr awt he el ect r onsi nacov al entbondt owar di t sel f . Fori oni cbonds,el ect r onegat i v i t ydi f f er encei sl ar ge( 23) ;f orcov al entbonds,t hedi f f er ence i ssmal lorev enzer o.I ft hedi f f er encei s0t o0. 5,i ti spur e,nonpol arcov al ent .I ft he di f f er encei s0. 52, i ti spol arcov al ent . Per centI oni cChar act er Wecanhav eamor equant i t at i v edescr i pt i onofachemi calbondbycal cul at i ngt he%i oni c char act er( %I )oft hebond.Thehi ghert he%i oni cchar act erofabond, t heeasi eri twi l lbet o br eak. 2 %I=16[ ∆EN]+3. 5( ∆EN) Exampl e:Cal cul at et he%i oni cchar act erf oreachoft hef ol l owi ngbonds:( a)Li F( b)CH ( c) OH Apol arcov al entmol ecul ehasadi pol e( oneendi sposi t i v eandt heot heri snegat i v e,bot h + char gessepar at edbyaf i xeddi st ance.Wecani ndi cat epol ar i t ybyusi ngt hesy mbol sδ and δ-, whi chi ndi cat epar t i al +and–char ges.Forexampl e, Hδ+Fδ Toshowt hatamol ecul ehasadi pol e,wemayal souset hi ssy mbol , poi nt sf r om posi t i v et onegat i v e. δ- δ+ CH δ-δ+ OH δ+ δCCl ,wher et hear r ow δ-δ+ CLi Exampl es: Twooft hemostcommonbondsi nor gani cchemi st r yar enonpol ar :car boncar bonand car bonhy dr ogen. 1. 4. 3. 8BondLengt handBondAngl e St r uct ur esofsmal lmol ecul escanal sobedescr i bedi nt er msofbondl engt hsandbond angl es.Bondl engt hi st heopt i mum di st ancebet weent henucl ei oft wobondedat oms. Bondi ngnucl eishoul dnotbet oocl ose( t oav oi dr epul si on)orbet oof arapar t( sot hatt he 10 bondi ngel ect r onsar eshar ed) .Bondl engt hi sexpr essedi nAngst r oms( Ả) .1Ả=10 m = 100pm. Abondangl ei st heangl eofar cbet weenanyt wobondst hatj oi nt hesameat om. 9 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 1. 4. 3. 9Resonance Thest r uct ur esofsomecompoundsandi onscannotber epr esent edbyasi ngl ef or mul a. Let ’ sconsi dersul f urdi oxi def orexampl e: Exper i ment alev i denceshowst hatal lSO bondshav eequall engt h( 1. 432Ả) .Hence,t he act ualst r uct ur er esembl esanav er ageoft het wo f or mul as.Theav er agi ngofel ect r on di st r i but i onov ert woormor ehy pot het i calst r uct ur es( canoni calf or ms)t opr oduceahy br i d el ect r oni cst r uct ur ei scal l edr esonance. Theonl ydi f f er encebet weenr esonancef or msi si nt hepl acementoft hei rπandnonbondi ng el ect r ons.Theat omst hemsel v esoccupyexact l yt hesamepl acei nbot hr esonancef or ms, andt heconnect i onsbet weent hem ar et hesame.Thepr obl em i st hatr esonancef or mscan’ t ber epr esent edonpaper . Sampl ePr obl ems 1. Dr awt hr eer esonancef or msf ort hecar bonat ei on, CO32-. 2. Dr awasmanyr esonancest r uct ur esasmaybepossi bl ef oreachoft hef ol l owi ng: ( a)For mi caci d, HCO2H ( b)For mat ei on, HCO2- ( c)Ni t r omet hane, CH3NO2 1. 5I nt er mol ecul arFor ces Manyoft hephy si cal char act er i st i csofcompoundst hatar eusedt oi dent i f yt hem ( e. g. , m. p. , b. p. , andsol ubi l i t y )ar eduet oi nt er mol ecul ari nt er act i ons, especi al l yf orsol i dsandl i qui ds. v anderWaal sat t r act i on:t heat t r act i v ef or ceat omsandmol ecul eshav ef orone anot her .I t ’ sduet ot heel ect r ost at i cat t r act i onofel ect r onsofonemol ecul eorat om f ort henucl eiofanot her .I ft her ewer enov anderWaal sf or ces,al lmat t erwoul d exi sti ngaseousst at e.Ther ear eal so I nt er mol ecul arf or ces-smal l err epul si v ef or cesbet weenmol ecul est hati ncr ease r api dl yatv er ysmal l i nt er mol ecul ardi st ances. . Cl assi f i cat i onofi nt er mol ecul arf or cesdependsont hest r uct ur e:di pol edi pol ei nt er act i ons, Londondi sper si onsandhy dr ogenbondi ng. 1. 5. 1Di pol eDi pol eFor ces 10 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Exi stbet weenpol armol ecul es-posi t i v eendofonemol ecul eal i gnswi t hnegat i v eendof anot hermol ecul e. Lowerener gyt hanr epul si on; sonetf or cei sat t r act i v ef or ce. 1. 5. 2 LondonDi sper si on Exi stbet weennonpol armol ecul es. Tempor ar ydi pol edi pol ei nt er act i ons. Lar gerat omsar emor epol ar i zabl e. Br anchi ngl ower sb. p.becauseofdecr easedsur f acecont actbet weenmol ecul es. 1. 5. 3Hy dr ogenBondi ng Occur swhent hehy dr ogenf r om onemol ecul ei sst r ongl yat t r act edt oal onepai rofel ect r ons ont heot hermol ecul e. Mostpower f ul i nt er mol ecul arf or cei nf l uenci ngneut r al ( unchar ged)mol ecul es. Ast r ongdi pol edi pol eat t r act i on, andt hemol ecul ei nv ol v edmusthav eNHorOHbond.OH bei ngmor epol art hanNH showsast r ongerhy dr ogenbondi scal l edadonor ,whi l et he mol ecul et hatpr ov i dest heel ect r onr i chsi t et owhi cht hehy dr ogeni sat t r act edi scal l edan accept or . Wat erandal cohol smayser v easbot hdonor sandaccept or s; et her s, al dehy des, ket onesand est er scanf unct i ononl yasaccept or s. St r ongert hehy dr ogenbond,t hehi ghert heboi l i ngpoi nt .1o and2o ami nesar ebot hdonor s andaccept or s, but3oami nesf unct i ononl yasaccept or s. 1. 5. 3 Sol ubi l i t y Li kedi ssol v esl i ke-pol arsol ut esdi ssol v ei npol arsol v ent s;nonpol arsol ut esdi ssol v ei n nonpol arsol v ent sduet oweaki nt er mol ecul arf or ces. Mol ecul eswi t hsi mi l ari nt er mol ecul arf or ceswi l l mi xf r eel y . I oni csol ut esdi ssol v ei npol arsol v ent s( e. g.H2O)bymeansofhy dr at i onoft hei onsoft he sol ut e.Abi l i t yofH2Ot osol v at ei onsandahi ghdi el ect r i cconst antmakest hi spossi bl e. Manyor gani ccompoundsar enear l yi nsol ubl ei nwat erandt hosewhi char esol ubl ear e hy dr ogenbondaccept oranddonorgr oups. 11 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 SAMPLEPROBLEMS 1. Whi chi sexpect edt ohav eahi gherboi l i ngpoi nt ?Why ?( a)CH3CH2OHorCH3CH2NH2 2.Est i mat et heboi l i ngpoi ntor der( 1f orhi ghestboi l i ngt o8f orl owestboi l i ngpoi nt )i neachof t he f ol l owi ngcompounds: 3.Fort hecompoundsbel ow, answert hef ol l owi ngquest i ons: ( a)Whi chcompoundsmayser v eonl yasHbondaccept or s? ( b)Whi chmayser v ebot hasHbondaccept or sanddonor s? ( c)Whi chwi l l notpar t i ci pat ei nHbondi ng? 4.Foreachgr oupofcompounds, i dent i f yt hosewhi char ecompl et el ywat ersol ubl e, i nsol ubl ei n wat er par t i al l ywat ersol ubl e: 1. 6Aci di t yandBasi ci t y 12 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Theaci dbasebehav i orofor gani cmol ecul eshel pst oexpl ai nmuchoft hei rchemi st r y . 1. 6. 1Var i ousDef i ni t i ons Ar r heni usdef i ni t i on:Anaci di sasubst ancewhi chf unct i onsasasour ceofhy dr ogeni onsi n aqueoussol ut i on.Abasei sasubst ancewhi chf unct i onsasasour ceofhy dr ox i dei onsi n aqueoussol ut i on.Thest r engt hofanaci di sr el at edt ot heeasewi t hwhi chi tf unct i onsasa sour ceofH+; t hest r engt hofabasei sr el at edt ot heeasewi t hwhi chi tf unct i onsasasour ce ofOH. Br onst edLowr yDef i ni t i on: Aci di saH+( pr ot on)donor .Basei saH+accept or . Br onst edLowr yDef i ni t i on: Aci di saH+( pr ot on)donor .Basei saH+accept or . St r ongaci dshav el ar gerKa’ st handoweakeraci ds.St r ongbaseshav el ar gerKb’ st hando weakerbases.Amor ef r equent l yusedquant i t yi st hepKaorpKb( t henegat i v el ogofKaor Kb, r espect i v el y ) .Thest r ongeranaci dorbase, t heweakeri t sconj ugat e.Aci dbaseequi l i br i a al way sf av ort heweakestaci dandt heweakestbase. Sampl ePr obl em:Pr edi ctt her el at i v eaci di t yof :( a)CH3OHandCH3NH2 ( b)CH3OHandCH3SH( c) + + H30 andNH4 . Lewi sdef i ni t i on:Anaci di sanel ect r onpai raccept orandabasei sanel ect r onpai rdonor . Lewi saci dsar e“ el ect r onl ov i ng”r eagent sorel ect r ophi l esandconsequent l yt endt or eact wi t hel ect r onr i chor“ nucl eusl ov i ng”r eagent scal l ednucl eophi l es( whi char eLewi sbases) . Sampl ePr obl ems 13 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 1. I neachoft hef ol l owi ngr eact i ons,i dent i f yt heLewi saci dandLewi sbase.Wher emor et han oneat om ofapar t i cul arr eagentcoul dbet hesi t eofr eact i v i t y ,i ndi cat ewhi chst r uct ur al f eat ur ei sr esponsi bl ef ort heact i v i t y . + ( a)( CH3) =C( CH3) 3C +H2C 2 + ( CH3) CH2C( CH3) 3C 2 ( b)( CH3) =C( CH3) H3 2C 2 +B ( CH3) HCH( CH3) H2 2C 2B 2. Cl assi f yeachoft hef ol l owi ngasanel ect r ophi l e( E) ,anucl eophi l e( Nu) ,ornei t her :( a) + ( CH3) b)( CH3CH2) H+ ( c)( CH3) d)( CH2) H+ ( e)CH3Li( f )CH3OH 3N ( 2C 4N ( 5C 3. Whi chi st hest r ongeraci doft hepai r :( a)H3O+orH2O;( b)NH4+orNH3;( c)H2SorHS-;( d) H2OorOH ? 14 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 TOPI C2: SATURATEDHYDROCARBONS–ALKANESANDCYCLOALKANES 2. 1Repr esent i ngOr gani cCompounds–St r uct ur al f or mul as Manyor gani ccompoundshav ecompl exst r uct ur es. Hence,shor t hand met hodshav e been dev el oped t or epr esentt hese compounds.The v ar i ousr epr esent at i onsar e:compl et est r uct ur alf or mul a,condensedst r uct ur alf or mul a,l i ne f or mul aandpol y gonf or mul a( i far i ngi si nv ol v ed) . Consi dert hecompound, t r i but y l car bi nol , C13H28O. Pr obl ems 1. Wr i t et hecondensedf or mul aandt hemol ecul arf or mul af or : 2. Wr i t et hecondensedf or mul af oranal kane, C28H58. 2. 2Funct i onal Gr oups St r uct ur al f eat ur est hatmakei tpossi bl et ocl assi f ycompoundsbyr eact i v i t y . A gr oup ofat oms( ot hert han CH orCC si ngl ebond)wi t hi n a mol ecul et hathasa char act er i st i cchemi calbehav i orandt husunder goesachangedur i ngt hecour seofa r eact i on. Thr ee( 3)br oadcl assesofor gani ccompoundsar er ecogni zed:hy dr ocar bons,compounds 15 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 cont ai ni ngoxy genandcompoundscont ai ni ngni t r ogen. CompoundsCont ai ni ngOxy gen CompoundsCont ai ni ngNi t r ogen CompoundsCont ai ni ngHal ogensorSul f ur 16 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2. 3Di st i ngui shi ngCar bonAt oms Car bon at oms i n a mol ecul e may be di st i ngui shed on t he basi s oft hei rst r uct ur al char act er i st i cs. Apr i mar y( 1o)car boni sbondedt onomor et hanoneot hercar bonat om.Asecondar y( 2o) o o car boni sbondedt ot woot hercar bonat oms,andt er t i ar y( 3)andquat er nar y( 4)car bon at omsar ebondedr espect i v el yt ot hr eeandf ourot hercar bons. 2. 4Sat ur at edHy dr ocar bons Sat ur at edhy dr ocar bonsar eal socal l edpar af f i ns.Theyi ncl udeal kanesandcy cl oal kanes. Theyar ecal l ed“ sat ur at ed”becauset heH/ Cr at i oi nt hesecompoundsi satamaxi mum si nceal l f ourv al encesofeachcar bonat om wer esat i sf i edbybondst oot herat oms. 2. 4. 1Al kanes-Met hane Gener al f or mul a: CnH2n+2 Thef or mul asandst r uct ur esoft heseal kanesi ncr easeuni f or ml ybyCH2 i ncr ement .A uni f or mv ar i at i onoft hi ski ndi naser i esofcompoundsi scal l edahomol ogousandeach compoundi nt heser i esi sahomol og.Ev er yhomol ogousser i eshasachar act er i st i cf or mul a. Thesi mpl estal kanei smet hane, aonecar bonal kane, wi t hf or mul a, CH4. Met hanei st hemostabundant , occur r i ngi nl ar geamount si nourat mospher e, i nt hegr ound andi nt heoceans, andev enonsomeot herpl anet s.I tconst i t ut es97%ofnat ur al gasandcan exi stasmar shgasbubbl i ngt ot hesur f aceofswamps. Met haneandal lt heal kaneswi t h4car bonsorl essar egasesatr oom t emper at ur eand at mospher i cpr essur e.Duet ot heweakv anderWaal ’ sf or cesofat t r act i on,t heseal kanes ( l oweral kanes)hav el owmel t i ngandboi l i ngpoi nt s.B. p. : met hane<et hane<pr opane Met hanei scol or l ess, andwhenl i quef i ed, i sl essdenset hanwat er .I t ’ sonl ysl i ght l ysol ubl ei n wat er . Met haner eact sonl ywi t hhi ghl yr eact i v esubst ancesorunderv er yv i gor ouscondi t i ons. 1. Oxi dat i on 17 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2. Hal ogenat i on: Heatorl i ghti sr equi r ed.React i v i t yofX2:F2>Cl Br >I sunr eact i v e.React i onwi t h 2> 2( 2)–I 2i chl or i nei scal l edchl or i nat i on( asubst i t ut i onr eact i on) . Wecancont r olt heabov er eact i onsot hatmonochl or i nat i onoccur s,y i el di ngonl yCH3Cl . Thi si saccompl i shedbyusi ngal ar geexcessofmet hane( notj ustbyi nt r oduci ng1mol eof Cl .Br omi nat i ont akespl aceathi ghert emper at ur esorwi t hUVl i ghtsomewhatl essr eadi l y 2) t hanchl or i nat i on,andi odi nat i oni si mpossi bl e.Fl uor i nat i oni ssov i gor oust hatev eni nt he dar kandatr oom t emper at ur e, t her eact i onmustbecar ef ul l ycont r ol l ed, andt hi si sdoneby di l ut i ngt her eact ant swi t hani ner tgasatl owpr essur e. The bel ow r eact i on mechani sm i s pr oposed f ort he chl or i nat i on ( orbr omi nat i on)of met hane;i tev enhol dsf ort hehal ogenat i onsofot heral kanes.Ar eact i onmechani sm i sa det ai l ed, st epby st ephy pot het i cal descr i pt i onofachemi cal r eact i on. Homol y si sofchl or i ney i el dst heext r emel yr eact i v ef r eer adi cal( anat om orgr oupofat oms possessi nganodd/unpai r edel ect r on) .Thechl or i nat i onofmet hanei sachai nr eact i on–a r eact i ont hati nv ol v esaser i esofst eps,eachofwhi chgener at esar eact i v esubst ancet hat br i ngsaboutt henextst ep. The1stst ep: chai ni ni t i at i ngst ep–ener gyi sabsor bed; ar eact i v epar t i cl ei sgener at ed. Thenextst eporst epsar echai npr opagat i ngst eps–ar eact i v epar t i cl ei sconsumedand anot herr eact i v epar t i cl ei sgener at edi neachoft hesest eps. 18 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 The st eps abov e ar er epeat ed unt i lf i nal l y ,t he chai nt er mi nat i ng st eps – r eact i v e par t i cl esar econsumedbutnotgener at ed–t wor eact i v epar t i cl esr eactandconsume eachot heroroneoft hem i scapt ur edbyt hewal l soft hev essel . Ani nhi bi t orsl owsdownorst opsar eact i oni fpr esenti nsmal l amount s.Anex ampl ei s oxy gen.I nt hi sex ampl e, oxy genr eact swi t ht hemet hy l r adi cal t of or m anew, l ess r eact i v ef r eer adi cal . 2. 4. 2St r uct ur esofOt herAl kanesandI somer i sm Somest r ai ght chai norunbr anchedal kanesar el i st edbel ow: #OfCAt oms Name #OfCar bonAt oms Name 1 Met hane 13 Tr i decane 2 Et hane 14 Tet r adecane 3 Pr opane 20 Ei cosane 4 But ane 5 Pent ane 22 Docosane 6 Hex ane 30 Tr i acont ane 21( 1+20) Heni cosane 7 Hept ane 31( 1+30) Hent r i acont ane 8 Oct ane 32( 2+30) Dot r i acont ane 9 Nonane 40 10 Decane 50 11 Undecane 100 12 Dot et r acont ahect ane Dodecane Tet r acont ane Pent acont ane Hect ane 142( 2+40+100) 19 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Al l CCandCHbondsar et hesamei nl engt handangl e. I somer i sm canexi stamongal kanesf r om C4andupwar ds.I somer i sm i st heexi st enceof mor et hanonest r uct ur ef oramol ecul arf or mul a.Compoundst hatar est r uct ur al l ydi f f er ent , butwhi chshar et hesamemol ecul arf or mul aar ecal l edi somer s. nBut ane and i sobut ene ar e const i t ut i onalorst r uct ur ali somer s( t hey di f f eri nt he connect i v i t yoft heat oms) .I sobut anei sanexampl eofabr anchedchai nal kane( anal kane cont ai ni ngoneormor esi dechai ns) .Const i t ut i onali somer sv ar yi npr oper t i essi ncet hey v ar yi nst r uct ur es. C5H12i somer s: Sampl ePr obl em: Wr i t econdensedandbondl i nef or mul asf or( a)t hef i v ei somer i cC4H14al kanes.( b) t heei ghtchl or opent anes( C5H11Cl )( c)t heni nedi br omobut anes( C4H8Br ) . 2 2. 4. 3Nomencl at ur eofAl kanes Two( 2)way st onameor gani ccompounds:common( or“ t r i v i al ” )andsy st emat i c.Begi nni ng i n1892,chemi st sdev el opedasetofr ul esf ornami ngor gani ccompoundsbasedont hei r st r uct ur es,whi chwenow cal lt heI UPACr ul es.I naddi t i on,t heAmer i canChemi calSoci et y ( ACS) ,whi chpubl i shest hej our nal ,Chemi calAbst r act s,hasi t sownappl i cat i onsoft he I UPACr ul es.Thesubsetofnomencl at ur ei susual l yknownast heCAS® nomencl at ur e.CAS® si mpl yappl i est heI UPACr ul esmor est r i ct l yt hant heI UPACi t sel fi nt hemaj or i t yofcases. I UPACRul es: Est abl i sht her ootnamebyf i ndi ngt hel ongestcont i nuouschai nofcar bonat omspr esenti n t hemol ecul e. 20 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 I ft wodi f f er entchai nsofequal l engt hsar epr esent , chooset heonewi t ht hel ar gernumberof br anchpoi nt sast her ootname/ par entchai n. Numbert heat omsi nt hemai nchai nbegi nni ngatt heendnear ert hef i r stbr anchpoi nt . I ft her ei sbr anchi ngatanequal di st anceawayf r om bot hendsoft hepar entchai n, begi n number i ngatt heendnear ert hesecondbr anchpoi nt . Assi gnanumbert oeachsubst i t uentaccor di ngt oi t spoi ntofat t achmentont hemai nchai n. Asubst i t uenti sanal ky lsi dechai norot herat omsorgr oupsat t achedatapoi ntt ot hemai n chai n.Anal ky lgr oupl acksoneoft hehy dr ogenat omsofanal kane.Soi ti snamedby r epl aci ngt hesuf f i x–anewi t h–y l .Forex ampl e, met hy l f orCH3, et hy l f orCH3CH2, et c. I ft her ear et wosubst i t uent sont hesamecar bon, gi v et hem bot ht hesamenumber . I ft woormor ei dent i calsubst i t uent sar epr esent ,useoneoft hemul t i pl i erpr ef i xesdi ,t r i , t et r a,et c.I ft woormor edi f f er entsubst i t uent sar epr esent ,ci t et hem i nal phabet i calor der . Thepr ef i xesar enotusedf oral phabet i z i ng.Usehy phenst osepar at et hedi f f er entpr ef i xes, andusecommast osepar at enumber s.Thenwr i t et henameasasi ngl ewor d. 21 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Whent her ei sasubbr anchedsubst i t uent ,i tmustbenamedf i r st .Thi scompl ex,subbr anchedsubst i t uenti snamedj ustast houghi twer ei t sel facompound.Number i ngoft hi s compl exsubst i t uentbegi nsatt hepoi ntofat t achmentt ot hemai nchai n.Thesubst i t uenti s al phabet i zedaccor di ngt ot hef i r stl et t erofi t scompl et ename( i ncl udi nganynumer i cal pr ef i x)andsetof fi npar ent hesi swhennami ngt hecompl et emol ecul e.Thenumber sont he compl exal ky l gr oupsar edi st i ngui shedf r om t hoseont hemai nchai nbyusi ng1’ , 2’ , et c. Somebr anchedchai nal ky lgr oupshav especi al( t r i v i al )nameswhi char eal l owedbyI UPAC, butnotbyCAS®. SAMPLEPROBLEMS 1. Gi v et heI UPACnamesoft hef ol l owi ng: 22 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2. Dr awt hest r uct ur esf ort hef ol l owi ng: ( a)2, 6, 10, 14t et r amet hy l hexadecane ( b)5( 1, 2di met hy l pr opy l ) 2met hy l nonane ( c)2, 2, 3t r i met hy l pent ane 3. Dr awl i nef or mul af oreachoft hef ol l owi ng:( a)2, 4, 6, 8t et r amet hy l nonane ( b)5® ® i sobut y l decaneWhi choft hesehasawr ongCAS name?Gi v ei t scor r ectCAS name. 2. 4. 4Nomencl at ur eofCy cl oal kanes Cy cl i c al i phat i c hy dr ocar bons ar e named by pr ef i xi ng cy cl o-t ot he name of t he cor r espondi ngopenchai nhy dr ocar bonhav i ngt hesamenumberofcar bonat omsast her i ng. Gener al f or mul a: CnH2n Cy cl oal kanesconsi stofr i ngsof–CH2-uni t s. Rul esf orNami ngCy cl oal kanes Becauset her ear enoendsi nacy cl i ccompound,t heCat om at t achedt ot hesubst i t uenti s assi gnedposi t i on1; hence, anumbert odesi gnat ei t sposi t i oni sunnecessar y . Thel ongestchai ncanei t herbet her i ngcar bonat omsort heal ky l gr oupat t achedt oi t . 23 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Number i ngbecomesnecessar yi ft her i ngcont ai nst woormor egr oupsandi tbegi nswi t h oneoft hesubst i t ut edr i ngcar bonat omsandcont i nuesi nt hedi r ect i ont hatgi v est hel owest possi bl enumber st ot heot her .I nt hename, t hegr oupsar el i nkedi nal phabet i cal or der . Hy dr ocar bonshav i ngmor et hanoner i ngar ecommon,andar egener al l ycal l edpol y cy cl i c compounds,speci f i cal l yr ef er r edt oasbi cy cl i c( t wor i ngs)ort r i cy cl i c( t hr eer i ngs) .Fora hy dr ocar boncont ai ni ngncar bonat omswi t hm r i ngs, t hef or mul ai s: CnH(2n+2-2m). Ther ear ef ourt y pesofbi cy cl oal kanesandeacht y pei snamedi naspeci al way I sol at edRi ngs–Ther ear enocommonat oms; t het wor i ngsar ej oi nedbya car boncar bonsi ngl ebond.Thecompoundoft hi st y pei snamedbyusi ngbot hof t her i ngsy st ems. Spi r oRi ngs–Thet wor i ngsshar eonecommonat om;t hecompoundoft hi st y pe i snamedbyusi ngt hepr ef i xspi r owi t ht henameoft hepar enthy dr ocar bon.I t ’ s namedasspi r o[ n. m] al kane,wher enandm ar et henumberofcar bonat omsi n eachbr i dge( excl udi ngt hespi r oat om) . 24 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Thepar entnamei sobt ai nedbycount i ngt het ot al#ofCat omsi nal lt her i ngs. The#si nt hebr acket si ndi cat et henumberofcar bonat omsoneachsi deoft he commoncar bonat om.Thenumber i ngi sdonest ar t i ngf r om skel et alcar bonof smal lr i ngandcont i nuedupt ot hespi r ocar bon.Thent heskel et alcar bonsi nt he l ar gerr i ngar enumber ed. Fused/ Condensedr i ngs–Thet wor i ngsshar eonecommonsi de/ bond( i . e. , t her e ar et wocommonat omswhi char eadj acentt oeachot her ) .Tonamet hi st y peof compound,f i r stdesi gnat et hebr i dgeheadcar bonat oms( at omsateachendof ev er ysect i onoft hemol ecul ecommont ot het wor i ngs) .Number i ngbegi nsatone br i dgehead, t henpr oceedsar oundt hel ongestbr i dgef i r stt ot heot herbr i dgehead at om,andt hencont i nuesal ongt he2ndl ongestbr i dgebackt ot he1stbr i dgehead, andf i nal l y ,f r om t he1st br i dgeheadt ot he2nd usi ngt heshor t estbr i dge( t he commonsi de) .The#sofCat om bet weent hebr i dgeheadcar bonsi nt hesy st em ar ei ndi cat ed by count i ng f r om t he br i dgehead car bon and l i st i ng t hem i n decr easi ngor deri nbr acket s.Thewor dbi cy cl ei spr ef i xedwi t ht hepar entname. Br i dgedRi ngs–Thet wor i ngscont ai nmor et hanonecommonsi de/ bond( i . e. , t her ear emor et hant wocommonat omswhi char eadj acentt oeachot her ) . Cer t ai n pol y cy cl i c hy dr ocar bons cont ai ni ng many r i ngs bei ng of st r ai ned st r uct ur esar eof t ennamedont hebasi soft hei rshapes. Sampl ePr obl ems( Pr act i ce) 1. Namet hesebyt heI UPACandbyt heCAS® wher eappl i cabl e: 25 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2. Dr awst r uct ur esf ort hef ol l owi ng:a)3chl or o1, 1di met hy l cy cl ohexane( b) 1chl or o1cy cl obut y l 4, 4di et hy l cy cl ohept ane ( c) 1, 1di met hy l cy cl ooct ane( d)bi cy cl o[ 6. 3. 0] undecane ( e)spi r o[ 3. 3] hept anes ( f )1cy cl obut y l 3cy cl opent y l hexane 3. Whi choft hef ol l owi ngcompoundsar ei somer sofspi r opent ane? 2. 4. 5Sour cesofAl kanesandCy cl oal kanes Nat ur algas-especi al l yr i chi nmet haneandal socont ai nset haneandpr opane,al ongwi t h smal l eramount sofot herl owmol ecul ar wei ghtal kanes. Pet r ol eum – usual l yassoci at edwi t hpet r ol eum.Pet r ol eum i sal i qui dmi xt ur econt ai ni ng v ar i ous subst ances i ncl udi ng hy dr ocar bons,r oughl y hal fofwhi ch ar e al kanes and cy cl oal kanes. Cy cl oal kanesar eknownt ot hepet r ol eum i ndust r yasnapht hal enes. Nat ur algascont ai nsonl yt hemor ev ol at i l eal kanes–t hoseofl owMW; i tconsi st schi ef l yof met haneandpr ogr essi v el ysmal l eramount sofet hane, pr opaneandhi gheral kanes. Pet r ol eum i ssepar at edi nt ov ar i ousf r act i onsbydi st i l l at i on: C1C4hy dr ocar bonsdi st i l l at<20oC C5C6( pet r ol eum et her )di st i l l of fat2060oC C6C7( l i gr oi norl i ghtnapht ha) at60100oC C5C10( cy cl oal kanesandnat ur al gasol i ne)at40205oC C6C12( St r ai ght chai nhy dr ocar bon)at85200oC 26 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 C12C18( Ker oseneandar omat i cs)at175325oC C15C18( Heat i ngoi l )at300–400oC o C16C24( Lubr i cat i ngoi l )at400C C40( Par af f i nwax )-sol i d 25>C30( Asphal t )–r esi due Moder npet r ol eum r ef i ni ngal soi nv ol v est hef ol l owi ng: Cat al y t i cI somer i zat i on–conv er si onofst r ai ght chai nal kanesi nt obr anchedchai n ones. Cr acki ng – conv er si on ofhi ghermol ecul ar wei ghthy dr ocar bonst ot hemor e v ol at i l e, l ower mol ecul arwei ghtonesbyheat( t her malcr acki ng)orwi t ht heai dof cer t ai ncat al y st s( cat al y t i ccr acki ng) . Cat al y t i cRef or mi ng–conv er si onoft hehy dr ocar bonsi npet r ol eum t oar omat i c hy dr ocar bonsandhi ghl ybr anchedal kanes,bot hofwhi chshowl esst endencyf or knocki ngt hanunbr anchedal kanesandcy cl oal kanes. 2. 4. 6Phy si cal Pr oper t i esofAl kanesandCy cl oal kanes Boi l i ngPoi nt s:C1C4al kanesar eal lgasesatr oom t emper at ur e;C5C17ar el i qui dsandt hose ofC18ormor ear esol i ds.Eachaddi t i onal –CH2-gr oupcor r espondst oanappr oxi mat er i seof 25o30oi nboi l i ngpoi nt .Mor et hebr anchi ng, l owert heboi l i ngpoi ntf oral kaneswi t ht hesame Cn.Thi si sbecauset hesur f acear eai sr educed, t husr educi ngt hev anderWaal sf or ces, and hencet heboi l i ngpoi nt .Forcy cl oal kanes, t heboi l i ngpoi nt si ncr easer egul ar l yast her i ngsi z e o i ncr easesandar e1020Chi gherboi l i ngt hanopenchai nal kanes. Mel t i ngPoi nt s:Mel t i ngpoi nt sdependonpacki ngi nt hesol i dst at e.Ev ennumber edcar bon packbet t erand hav e hi ghermel t i ng poi nt .Mel t i ng poi ntr ef l ect st he st r engt h oft he i nt er mol ecul arf or cesi nacr y st al .Br anchi ngofanal kanegi v esi tamor ecompactt hr eedi mensi onalst r uct ur e,t husi ncr easi ngt hemel t i ngpoi nt .Al so,mel t i ngpoi nti ncr easeswi t h i ncr easi ngchai nl engt h.Forbot hal kanesandcy cl oal kanes, t hi si ncr ementi snotr egul ar . Sol ubi l i t y :Al kanesandcy cl oal kanesar enonpol ar ,andi nsomecasesv er yweakl ypol ar . Hence,t heyar ei nsol ubl ei npol arsol v ent ssuchaswat er ,al coholandacet one.Themost i nsol ubl ear et hosewi t hl ongercar bon chai ns.Hence,l ar gert hecar bon chai ns,mor e i nsol ubl ei ti si npol arsol v ent s.Nonpol arsol v ent sl i kebenzene, et her , chl or of or m andcar bon t et r achl or i dear eappr opr i at e. Densi t y :Theyar el essdenset han wat er ,ev en t hough t her ei san i ncr easei n densi t y cor r espondi ngt oi ncr easei nsi zeoft hemol ecul e.Howev er , t hehi ghestdensi t yi s0. 8. 27 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2. 4. 7Pr epar at i onsofAl kanesandCy cl oal kanes 2. 4. 7. 1Pr epar at i onofAl kanes Smal l eral kanes,C1C5 ( excl udi ngneopent ane)ar eobt ai nedi npur ef or m byf r act i onaldi st i l l at i onof pet r ol eum andnat ur al gas. 1.LabPr epar at i onofMet hane:Heat i ngsodi um acet at ei nt hepr esenceofsodal i me( ami xt ur eof CaOandNaOH)i nat estt ube. 2.Hy dr ogeneat i onofAl kenes: Ther eact i oni sexot her mi cbecauset het wosi gmabonds( CH)bei ngf or medar et oget herst r onger t hant hesi gmabond( HH)andπbondbei ngbr oken.Thoughexot her mi c, acat al y sti sneeded. 3.Reduct i onofAl ky l Hal i des: ( a)Byt r eat mentofal ky l hal i dewi t hami xt ur eofHIandr edphosphor usorLi Al H4. ( b)Reduct i onbymet al andaci d ( c)ByHy dr ol y si sofaGr i gnar dReagent Howi st heGr i gnar dReagentpr epar ed?Asol ut i onofanal ky lhal i dei ndr yet heri sal l owedt ost and ov erMgt ur ni ngs;v i gor ousr eact i onoccur sast hesol ut i ont ur nscl oudy ,begi nst oboi landt heMg met al gr adual l ydi sappear s. 28 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 4.TheKol beEl ect r ol y si s: El ect r ol y si sofanaqueoussol ut i onoft hesodi um sal tofacar boxy l i caci d. 5.TheWur t zReact i on: Mechani sm Twomechani smshav ebeensuggest ed–onei nv ol v i ngaf r eer adi cali nt er medi at eandt heot her i nv ol v i ngasodi um al ky l i nt er medi at e. Hy dr ocar bonswi t hanoddnumberofcar bonat omscannotbepr epar edbyt hi smet hodduet ot he f or mat i onofami xt ur eofhy dr ocar bonswhi chmaybedi f f i cul tt osepar at e.Forunsy mmet r i cal hy dr ocar bons,weuset heWur t zFi t t i gr eact i on–heat i nganal i phat i candanar omat i chal i dewi t h sodi um i nani ner tat mospher e. Mi xedpr oduct sar eobt ai ned, butcanbesepar at edont hebasi soft hei rphy si cal pr oper t i es. 6.Hy dr ogenol y si s: Cl eav ageofCX( X=hal ogen)bondi nt hepr esenceofH2andPtcat al y st . 29 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Li Al H4coul dbeusedi nst ead. 7.Hy dr obor at i onofAl kenes: 8.TheCor ey HouseSy nt hesi s: -Dev el opedi nt hel at e1960sbyE. J.Cor eyandHer ber tHouse. -Usedt omakeal kanesofhi gherC#t hant heor i gi nal mat er i al . -Bot hsy mmet r i cal andunsy mmet r i cal al kanescanbepr epar ed. -I nv ol v est hecoupl i ngofal ky lhal i deswi t hor ganomet al l i ccompounds;t woal ky lgr oups,RandR’ ar ecoupl ed;Rcomesf r om anor ganomet al l i ccompound,al i t hi um di al ky l copper ,R2CuLiandR’ comesf r om a1oal ky l hal i de, R’ X. 9.Fr om Al umi num Car bi de: Fort hepr epar at i onofmet hane. Al 2H2O 4C 3 +1 3CH4 +4Al ( OH) 3 2. 4. 7. 2Pr epar at i onofCy cl oal kanes 1.Act i onofmet al l i csodi um onωdi hal ogender i v at i v es. 30 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2.Conv er si onofbenzenet ocy cl ohexanebycat al y t i chy dr ogenat i on( Ni ,hi ght emper at ur eand pr essur e) . Orbydehy dr at i onofanal cohol , cy cl ohexanol 3.Cy cl opr opanat i on: Car benes r eactwi t h car boncar bon doubl e bonds t of or m cy cl opr opanes,t he pr ocess cal l ed cy cl opr opanat i on. 4.Thr ought heDi el sAl derReact i on: 5.TheSi mmonsSmi t hReact i on: 6.Fr om Gr i gnar dReagent s: 31 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2. 4. 8React i onsofAl kanesandCy cl oal kanes Theal kanesandcy cl oal kanes( exceptcy cl opr opane) , ar epr obabl yt hel eastr eact i v ecl assofor gani c compounds. 2. 4. 8. 1React i onsofAl kanes Despi t et hei rr el at i v ei ner t ness,al kanesdo under go sev er ali mpor t antr eact i onsunderdr ast i c condi t i ons. 1.Combust i on:Bur ni ngoft heal kanei nexcessoxy gent opr oduceCO2,H2Oandal ar geamountof heatener gy .I nt hi sway , al kanesser v easf uel si nt er nal combust i onengi nesorf ur nace. ∆H = 845 Kcal ( Heat of combust i on) I ft hesuppl yofox y geni si nadequat e, i ncompl et ecombust i onoccur s, pr oduci ngpoi sonousCO. 2.Ni t r at i on:Athi ght emper at ur es,al kanesr eactwi t hni t r i caci dt of or m ami xt ur eofni t r opar af f i ns usedt osy nt hesi zeexpl osi v esandassol v ent s. 32 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 3.Hal ogenat i on:React i onwi t hhal ogensundercont r ol l edcondi t i ons( i nt hepr esenceofei t her ul t r av i ol etl i ghtorathi gh t emper at ur es) .An except i on i st he case wher e Pb( C2H5) ni t i at es 4 i chl or i nat i onofCH4i nt hedar kduet ot hef or mat i onofC2H5r adi cal s. Or derofReact i v i t yofHal ogens, X2: F2>>Cl Br >>I 2> 2> 2 Basi cal l y ,hal ogenat i onoccur swi t hCl ndBr F2 i st oor eact i v et obeempl oy edandnor eact i on 2a 2occur swi t hI Howev er ,i thasbeenf oundi nr ecentt i mest hatwhenF2 i sdi l ut edwi t hani ner tgas, 2. andi nanappar at usdesi gnedt ocar r yawayt heheatpr oduced, t her eact i oncanoccursaf el y . I somer i cpr oduct s( mi xt ur e)usual l yexi stduet ot hepossi bi l i t yofabst r act i ng/ r epl aci ng1o,2o,3o or met hy l H. Easeofabst r act i onofHat oms: 3o>2o>1o>CH3H Chl or i nat i ongi v espr oduct si nwhi chnoi somergr eat l ypr edomi nat es;i nbr omi nat i on,t her e’ sahi gh degr eeofsel ect i v i t yduet ot hel ow r eact i v i t yofBrat oms.Ther el at i v epr opor t i onofpr oduct s dependsonhow f astt her adi cal sar ef or med.Fast ert hef or mat i onoft her adi cal ,gr eat ert he pr opor t i on. 33 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Mechani sm Thechl or i nat i onorbr omi nat i onpr oceedst hr oughaf r eer adi cal chai nmechani sm. 34 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Atr oom t emper at ur e,t her el at i v er at eofabst r act i onperhy dr ogenat om i namol ecul ei s5. 0: 3. 8: 1. 0 o o o i nt heor der3: 2: 1.Usi ngt hesev al ues,wecanpr edi ctt hepr opor t i onofi somer i cchl or i nat i on pr oduct sf r om agi v enal kane. 4.Cr acki ng ( Py r ol y si s) :Decomposi t i on ofacompound byt heact i on ofheatal one.Py r ol y si s i nv ol v i ngoror i gi nat i ngf r om pet r ol eum i sknownascr acki ng. 35 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 5.I somer i zat i on: Conv er si onf r om st r ai ght chai nt obr anchedchai n. 6.Cat al y t i cdehy dr ogenat i on: Passi ngRHv apor sov erCr at al y stwi t ht hel ossoft woHat oms. 2O3c 7.Ar omat i zat i on( Ref or mi ng) : Accompl i shedbyt heuseofahet er ogeneouscat al y st . 2. 4. 8. 2React i onsofCy cl oal kanes Wi t hcer t ai nv er yi mpor t antexcept i ons,al i cy cl i chy dr ocar bonsunder got hesamer eact i onsast hei r openchai nanal ogs. 1.Fr eer adi cal subst i t ut i on( chi efr eact i on) . 36 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2.Cy cl opr opaneandcy cl obut aneunder gocer t ai naddi t i onr eact i ons,y i el di ngopenchai npr oduct s. Howev er , cy cl obut anedoessol essr eadi l yt hancy cl opr opane. ( a)Hy dr ogenol y si sofcy cl opr opanes -Leastsubst i t ut edbondusual l yr eact s. ( b)El ect r ophi l i ccl eav ageofcy cl opr opane ( i )React i onwi t hhal ogensandsi mi l armol ecul es Her e, t hemor esubst i t ut edr i ngbondbr eaks; mor eel ect r onegat i v eat om ofr eagentendsupbonded t ot hemor esubst i t ut edendoft her i ngat om. Reagent s: Cl FeCl Br CCl I Cl ; Br Cl ; HOBr ; HOCl ; et c. 2/ 3; 2/ 4; 37 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 ( i i )React i onwi t hpr ot onaci ds Mostsubst i t ut edr i ngbondbr eaks,hy dr ogenat om oft heaci dendsupbondedt ol esssubst i t ut ed endoft her i ngbond. 3.Cy cl ohexanei soxi di zedt ocy cl ohexanol i nt hepr esenceofdi met hy l di oxi r ane. SAMPLEPROBLEMS 1.Wi t houtr ef er r i ngt ot abl es, l i stt hef ol l owi nghy dr ocar bonsi nor derofdecr easi ngboi l i ngpoi nt s: ( a)3, 3di met hy l pent ane( b)nhept ane( c)2met hy l hept ane( d)npent ane( e)3met hy l hexane 2.( a)Whi chal kanewoul dy ouex pectt ogetbyt heact i onofwat eronnpr opy l magnesi um chl or i de? ( b)oni sopr opy l magnesi um chl or i de?( c)Answer( a)and( b)f ort heact i onofdeut er i um ox i de, D2O. 3.Onconv er si oni nt ot heGr i gnar dr eagentf ol l owedbyt r eat mentwi t hwat er ,how manyal ky l br omi deswoul dy i el d:( a)npent ane( b)2met hy l but ane( c)2, 3di met hy l but ane( d)neopent ane? Dr awst r uct ur esi neachcase. 4.Out l i net woconcei v abl esy nt hesesof2met hy l pent anef r om 3car boncompounds.( b)Whi chof 38 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 t het wowoul dy ouact ual l yuse?Why ? 5.Wr i t ebal ancedequat i ons, nami ngal l or gani cpr oduct s, f ort hef ol l owi ngr eact i ons: ( a)t Bubr omi de+Mg/ et her( b)pr oductof( a)+H2O( c)secBuchl or i de+Li , t henCuI ( d)pr oductof( c)+et hy l br omi de 6.Wr i t eequat i onsf ort hepr epar at i onofnbut anef r om: ( a)nbut y l br omi de( b)secbut y l br omi de( c)et hy l chl or i de( d)2but ane, CH3CH=CHCH3 7.Thef i nalst epi nt hepr oofofst r uct ur eofanunknownal kanewasi t ssy nt hesi sbyt hecoupl i ngof l i t hi um di ( t Bu) copperwi t hnbut y l br omi de.Whatwast heal kane? 8.Dr aw st r uct ur esoft he( a)t hr eemonochl or oder i v at i v esofnpent ane( b)f ourmonochl or oder i v at i v esofi sopent ane. 9.Pr edi ctt hepr opor t i onsofi somer i cpr oduct sf r om chl or i nat i onatr oom t emper at ur eof :( a) pr opane( b)i sobut ene( c)2, 3di met hy l but ane( d)npent ane( NB.Ther ear et hr eei somer i cpr oduct s. ) ( e)i sopent ane 10.Foreachoft hef ol l owi ngal kanes/ cy cl oal kanes,i ndi cat ehow manymonohal ogenat edand t r i hal ogenat edconst i t ut i onali somer scoul dbepr oducedonr eact i onwi t h1t o3equi v al net sof hal ogen( Cl rBr : 2o 2) ( a)CH3CH2CH3( b)CH3CH2CH2CH3( c)( CH3CH2) d)( CH3) HCH( CH3) 4C( 2C 2 11.Asat ur at edhy dr ocar bonbur nsi nox y gent ogi v ecar bondi ox i deandwat er .Appr oxi mat el yt wi ce asmuchCO2asH2O( bywei ght )i spr oduced, t heact ualf act orbei ng2. 03.Li ghti nducedchl or i nat i on oft hehy dr ocar bonby2. 0equi v al ent sofchl or i negi v esami xt ur eofmono,di -andt r i chl or o compounds, al ongwi t hsmal lamount sofhi gherchl or i nat i onpr oduct s.Onl yonemonochl or oi somer i sf or med,butt her ear et wodi chl or oi somer sandt hr eet r i chl or oi somer spr oducedi nt her eact i on. Basedont hi si nf or mat i on,i dent i f yt hehy dr ocar bonbywr i t i ngi t smol ecul arf or mul aandi t sI UPAC name. 12.Wr i t et hecompl et er eact i onmechani sm f ort hef or mat i onof2br omo2met hy l pr opanebyt he f r eer adi cal br omi nat i onof2met hy l pr opane. 13.Whatdoesi tmeanwhenwesayacer t ai ngasol i nepr oducthasanoct aner at i ngof85? 14.Gi v er easonsf ort hef ol l owi ng: ( a)Oct anehasam. p.of57o, whi l e2, 2, 3, 3t et r amet hy l but anehasam. p.of101o. ( b)A3of r eer adi cal i smor eeasi l yf or medt hana1of r eer adi cal . 39 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 ( c)Et hanol ( et hy l al cohol )i ssol ubl ei nwat er , butet hanei snot . ( d)Met hanei smor est abl et hanot herhi gheral kanes. ( e)Thequal i t yofaf uel i si mpr ov edbyt headdi t i onoft et r aet hy l l ead. 15.Wr i t et hepr oduct sofeachr eact i on: 16.I ndi cat e( wi t happr opr i at eequat i ons)t hr eedi f f er entmet hodsf ort heconv er si onofi sobut y l br omi det oi sobut ene. 17.Wr i t eabal ancedequat i onf ort hecompl et ecombust i onofnbut ane. 18.A hy dr ocar bonA,wasf oundt ohav eav apordensi t yof36.I tf or msonl yonemonochl or o subst i t ut i onpr oduct s.I dent i f yA. 19.Pr epar enhexanef r om nbut y l i odi de. 20.Howwoul dy oubr i ngaboutt hef ol l owi ngconv er si ons: 21.Compl et et hef ol l owi ngr eact i ons: 40 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 22.Pr edi ctt hepr oduct sf oreachoft hef ol l owi ngr eact i ons: 41 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 TOPI C3: CONFORMATI ONSOFALKANESANDCYCLOALKANES Conf or mat i onsar edi f f er entspat i alar r angement sofamol ecul et hatar egener at edby r ot at i onaboutsi ngl ebonds. Conf or mat i onsar ei nt er conv er t i bl e; ot her wi set heywoul dbeconf i gur at i ons. Conf or mat i onsar er epr esent edbyconf or mer sorconf or mat i onali somer s( name gi v enbySi rWi l l i am Hawor t h)whi chcannotbesepar at ed, unl i keconf i gur at i ons. They ar e somet i mes cal l ed r ot at i onali somer s orr ot amer s because t hey ar e gener at edbyr ot at i on. Thepr oper t i esofconf or mer sar et hesame, unl i keconf i gur at i oni somer s. Thest udyofconf or mat i onofor gani cmol ecul es/ ananal y si soft heener gychanges t hatamol ecul eunder goesasgr oupsorat omsr ot at eaboutasi ngl ebondi scal l ed conf or mat i onal anal y si s. 3. 1Pr oj ect i onFor mul asandTy pesofconf or mat i ons Conf or mat i onsar er epr esent edbypr oj ect i onf or mul aswhi char emet hodsf orr epr esent i ng 3Dmol ecul esi nt wodi mensi ons.Ther ear ef i v e( 5)mostcommonl yusedpr oj ect i ons; namel y : sawhor se, Fi scher , Newman, dashwedge/ l i neandbowt i epr oj ect i ons.Thef ocus wi l l beonsawhor se, Fi scherandNewmanpr oj ect i ons. Sawhor sePr oj ect i on Fi scherPr oj ect i on–Thecent r alcar bonat om l i esi nt hepl aneoft hepaperandt he hor i zont albondsabov et hepl ane( t owar dst hev i ewer ) ,whi l et hev er t i calbondsar e bel owt hepl ane( awayf r om t hev i ewer ) . 42 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 NewmanPr oj ect i on–Themol ecul ewi t ht wot et r ahedr alcent er si sv i ewedal ongt he CCax i s( C1C2ax i s) , wi t hC1near ert ot hev i ewer , whi l eC2i sawayf r om t heey eandi s r epr esent edbyaci r cl e,andt heC1C2bondi snotseen.Al lt hr eeat oms( orgr oups) at t achedt oC1 r adi at easl i nesf r om t heC1 poi ntandt hoseat omsont heper i pher y r adi at ef r om C2. Thi si st he bestand mostusef ulpr oj ect i on i n consi der at i on ofst er i cr el at i on bet weent het et r ahedr al cent er sandt heat t achedat oms/ gr oups. Thedi f f er entt y pesofconf or mat i onar e: St agger ed–Thebul kygr oupsar easf arapar taspossi bl eandt heCHbondsar e r egul ar l yst agger edf r om f r ontcar bont obackcar bon. 43 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Ecl i psed–Thegr oupsar ecl osedt oget her ;al lt heCH bondsoft hef r ontcar bon at om exact l yov er l apwi t hal l t heCHbondsoft hebackcar bonat om. Ot hert y pessuchasgauche, ant iandsy nwi l l bedescr i bedl at er . 3. 2Conf or mat i oni nOpenChai nSy st ems Foranyopenchai nsi ngl ebondt hatconnect st wosp2car bonat oms, ani nf i ni t enumberof conf or mat i onsar epossi bl e, eachofwhi chhasacer t ai nener gyassoci at edwi t hi t . 3. 2. 1Conf or mat i onal Anal y si sofEt haneandBut ane Et hane:Ther ear eanumberofdi st i nctconf or mat i ons, t heecl i psedandt hest agger edbei ngt het wo ext r emes; Ecl i psedhast hehi ghestpot ent i al ener gyandst agger edhast hel owestpot ent i al ener gy . Ast hebondr ot at est owar dst heecl i psedconf or mat i on,i t spot ent i alener gyi ncr easesas t her ei sar esi st ancet or ot at i on.Thi st wi st i ng( t or si on)i scal l edt or si onalst r ai nandt he ener gydi f f er enceonr ot at i onf r om st agger edt oecl i psedi scal l edt or si onalener gy .For et hane, t or si onal ener gyi s2. 9kcal / mol e( 12. 0kJ/ mol e) . Ecl i psedbondshav e0ot or si onangl e; st agger edbondshav e60ot or si onangl ef ort hegauche conf or mat i onor180ot or si onangl ef ort heant i .St agger edconf or mat i onwi t hal owerener gy i smor est abl et hant heecl i psed.Thedest abi l i z at i ont hatr esul t sf r om ecl i psedbondson adj acentat omsi st or si onal st r ai n. 44 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 o Ѳ=Tor si onangl e, ( ) But ane: But anehasal ar gerandmor ecompl exsetofconf or mat i onsassoci at edwi t hi t sconst i t ut i on t hanet hane.Twoki ndsofst agger edandt woki ndsofecl i psedconf or mer sar eshownbel ow. Asi nt hecaseofet hane, t hemostunst abl econf or meri st hef ul l yecl i psedconf or mat i on. Ѳ=0o ѳ=60o ѳ=120o 45 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Ther ef or e, t heecl i psedconf or mat i onmaybef ul l orpar t i al , whi l et hest agger edconf or mat i on maybegaucheorant i .Theant ii smor est abl et hant hegauchebecauset wooft hemet hy l H’ sar ev er ycl oset oeachot herandt hus,t her ei sr epul si onbet weent hem.Thet or si onal ener gyf orbut aneconf or mat i oni s6. 1kcal / mol e( 25kJ/ mol e) . I I I I V P. E. ∆E I I I V VI 25KJ/ mol 0 60 120 180 240 300 360 o Ѳ=Tor si onangl e( ) 3. 2Conf or mat i onofCy cl oal kanes-Cy cl hexane Unl i ket heopenchai n al kanes,t hecy cl oal kanescannotadoptan unl i mi t ed numberof conf or mat i onsbecauseofconst r ai nt si mposedbyt her i ng. Thecy cl ohexaner i ngcanadoptanumberofconf or mat i ons,t het woext r emesbei ngt he chai rand t het wi storskew boat .Ther ear eal so t hehal f chai r( t wi stchai r )and boat conf or mat i onsbet weent het woext r emes.Bot ht heboatandt hehal f chai rhav ehi ghener gy , andt hus,ar eonl yt r ansi t i onst at econf or mat i onsbet weent het woext r emes,andar el ess st abl e.Thechai rconf or mat i oni st hemostst abl e–t her ear eper f ect l yst agger edbondsand not or si onal orangl est r ai n. 46 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Al lr i ngbondshav et hebut anegaucheconf or mat i on.Onecandr awt wochai rconf or mat i ons f ort hecy cl ohexaner i ng, andt her i ngcanunder goapr ocessknownasr i ngi nv er si onor“ r i ng f l i ppi ng”i n whi ch t hese conf or mer s ar ei nt er conv er t ed.The i nt er conv er si on pr oceeds t hr oughav er yhi ghener gyconf or mat i onoft her i ngknownast hehal f chai rconf or mat i on. Byf l i ppi ngt hechai rconf or mat i on,wegett heboatconf or mat i oni nwhi cht hebondsar e ecl i psed.Four( 4)pai r sofhy dr ogenat omsoccupyecl i psed posi t i ons.Hence,t her ei s consi der abl est r ai n.I naddi t i on,t her ei sv anderWaal sst r ai nbecauset wohy dr ogenat oms ont heendsoft heboat , r ef er r edt oas“ f l agpol e”hy dr ogensi nt er f er ewi t heachot her .Hence, t heboatf or mi smuchl essst abl et hant hechai rf or m.Asar esul t ,t heboatf or m maynot r eal l ybeaconf or mer , butat r ansi t i onst at ebet weent hechai randt heskewboat . Onex ami nat i onofachai rconf or mat i onofcy cl ohexane,wef i ndt he12hy dr ogenat omsar e notst r uct ur al l yequi v al ent .6oft hem ar edi r ect edupanddown, par al l el t ot heaxi soft her i ng. Thesear eaxi albondsand ar er epr esent ed byv er t i call i nes.Theot her6 bondspoi nt out war ds,f or mi ngr i ngal ongi t sper i pher y .Thesear ecal l edequat or i albonds.Eachcar bon hasoneequat or i al bondandoneaxi al bond. 47 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Becausechai rcy cl ohexanehast woki ndsofposi t i ons,axi alandequat or i al ,onemi ght expectt of i ndt woi somer i cf or msofamonosubst i t ut edcy cl ohexane.Ont hecont r ar y , t her e i sonl yonebecausecy cl ohexaner i ngsar econf or mat i onal l ymobi l eatr oom t emper at ur e. Ther ei si nt er conv er si onr ef er r edt oasr i ngf l i p( keepi ngt hemi ddl e4car bonat omsi npl ace whi l ef ol di ngt het woendsi nopposi t edi r ect i ons) . Ri ngf l i ppi ngmayal sober ef er r edt oasr i ngi nv er si onorchai r chai ri nt er conv er si on. SAMPLEPROBLEMS/ PRACTI CE 1. I dent i f yt heal kanescor r espondi ngt oeachoft hedr awi ngsbel ow: 2. Dr awt heNewmanpr oj ect i onal ongt hei ndi cat edbondf ort hel owestener gyconf or mat i onof 48 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 ( a)2, 2di met hy l but ane[ 2, 3bond]( b)hexane[ 3, 4bond]( c)4et hy l oct ane[ 4, 5bond] 3. Si ght i ngal ongt heC2C1bond,dr aw t heNewmanpr oj ect i onsof2met hy l pr opane.Dot he samef or1chl or opr opane. 4. Fort hef our ( 4)namedhy dr ocar bonsbel ow, t her ear esi xt een( 16)conf or mat i onalst r uct ur es At hr oughP.Sel ectt hest r uct ur est hatr epr esentpossi bl econf or mer sofeachhy dr ocar bon: ( i )2met hy l but ane( i i )2, 3di met hy l pent ane( i i i )1et hy l 1, 3di met hy l cy cl ohexane( i v )2et hy l 1, 1di met hy l cy cl ohexane 49 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 5. Gi v ent hef ol l owi ngpar t i alst r uct ur e,addasubst i t uentX t oC1sot hati tsat i sf i est he i ndi cat edst er eochemi cal r equi r ement . 6. I nt hecy cl ohexaner i ng( chai rconf or mat i on)shownbel ow:( a)I samet hy latC6t hati s “ down”axi alorequat or i al ?( b)I samet hy lt hati s“ up”atC1mor eorl essst abl et hana met hy lt hati s“ up”atC4?( c)Pl aceamet hy latC3i ni t smostst abl eor i ent at i on.I si tupor down? TOPI C4: ALKYLHALI DES Al ky lhal i desandal cohol sr ankamongt hemostusef ulcl assesofor gani ccompoundsbecauset hey of t enser v easst ar t i ngmat er i al sf ort hepr epar at i onofmanyot hercl assesofor gani ccompounds. 4. 1I nt r oduct i on Al sor ef er r edt oasor ganohal i desorhal oal kanes; Compoundsi nwhi chahal ogenat om i sbondedt oasat ur at edsp3hy br i di zedcar bon; Gener al f or mul a: RX; Xi st hehal ogenf unct i onal gr oup( F, Cl , Br , I ) ; Hal ogen at omsar emor eel ect r onegat i v et han t hecar bon at om;t her ef or et hecar bonhal ogenbondi spol ar i zed: El ect r onegat i v i t ydecr easesi nt heor derofF>Cl >Br>I ; soCXbondl engt hsi ncr easei nt he or derofCF<CCl <CBr<CI . Thechemi st r yofal ky lhal i desi sdomi nat edbyt hi sef f ectandusual l yr esul t si nt heCXbond bei ngbr oken( ei t heri nasubst i t ut i onorel i mi nat i onr eact i on) . 50 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Al ky l hal i desmaybecl assi f i edas1o, 2oor3oasshownbel ow: 4. 2Nomencl at ur eofAky l Hal i des I UPAC r ul esper mi tal ky lhal i dest o be named i nt wo di f f er entway s:f unct i onalcl ass nomencl at ur eandsubst i t ut i v enomencl at ur e.Thef unct i onalcl assnomencl at ur ei smor e f ami l i arandconv eni ent , butt hesubst i t ut i v ecl assi smor eI UPACandi spr ef er r ed. Fort hef unct i onalcl assnomencl at ur e,t heal ky lgr oupandt hehal i dear edesi gnat edas separ at ewor ds.Fort hesubst i t ut i v enomencl at ur e,hal ogeni st r eat edasahal o( f l uor o, chl or o, br omo, i odo)subst i t uentonanal kene. Hal ogenandal ky lsubst i t uenthav eequalr ank.Sowhenbot har ei nt hechai n,t hnumber i ng i sdonet ogi v et hel owernumbert ot hesubst i t uentnear ert heendoft hechai n. I fadoubl eort r i pl ebondi spr esent , t hepar entchai nmustcont ai ni t . I ft hepar entchai ncanbepr oper l ynumber edf r om ei t herendwhi chi snear ert hesubst i t uent , begi natt heendnear ert hesubst i t uentt hathasal phabet i cal pr ecedence. PRACTI CEPROBLEMS 1. Gi v et heI UPAC( subst i t ut i v e)namef ort hef ol l owi ngal ky l hal i des: 2. Dr awst r uct ur escor r espondi ngt ot hef ol l owi ngI UPACnames: ( a)2Chl or o3, 3di met hy l hexane ( b)1, 1Di br omoi sopr opy l cy cl ohex ane 4. 3Phy si cal Pr oper t i esofAl ky l Hal i des Boi l i ngpoi nti ncr easesasonedescendst hePer i odi cTabl e( RF<RCl <RBr <RI ) I nsol ubl ei nwat er Densi t y : RFandRCl ar el essdense, butRBrandRIar emor edenset hanwat er 4. 4Pr epar at i onofAl ky l Hal i des Fr om Al kanesVi aFr eeRadi calHal ogenat i on:React i onofanal kane( RH)wi t hCl rBr n 2o 2i t hepr esenceofl i ghtgi v esal ky lhal i desubst i t ut i onpr oduct .Usual l y ,t hi smet hodgi v esa mi x t ur eofmono, di , t r i , et c.hal ogenat edcompounds. X2 + RH RCl+ HX ( X=Cl orBr ) 51 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 PRACTI CE Gi v et hest r uct ur eoft hepr i nci palor gani cpr oductf or medbyt hef r eer adi calchl or i nat i onofeachof t he f ol l owi ng: ( a) Met hy l cy cl opent ane ( b) 1I sopr opy l 1met hy l cy cl opent ane ( c) 2, 2, Tr i mehy l pent ane Fr om Al kenesVi aAl l y l i cBr omi nat i on:Ther e’ ssubst i t ut i onofhy dr ogenbybr omi neatt he al l y l i cposi t i on–t heposi t i onnextt ot hedoubl ebond. Assi gnment : I l l ust r at eanaccept abl emechani sm f ort heabov er eact i on. Fr om Al kenesandAl ky nes( Pr ev i ousl ydi scussedunderAl kenesandAl ky nes) Fr om Al cohol s Or derofReact i v i t yofHX:HI>HBr>HCl >HF o Or derofReact i v i t yofROH: CH3OH<RCH2OH( I )<R2CHOH( 2o)<R3COH( 3o) React i onswi t ht hi ony lchl or i de( SOCl ndphosphor ust r i br omi de( PBr or mal l y 2)a 3)n occurr eadi l yundermi l d condi t i ons,and ar el essl i kel yt o causeaci dcat al y zed r ear r angement st hant heHXmet hod. PRACTI CEPROBLEMS 1. Howwoul dy oupr epar et hef ol l owi ngal ky l hal i desf r om t hecor r espondi ngal cohol s? 2. Wr i t echemi calequat i onsf ort her eact i ont hatt akespl acebet weeneachoft hef ol l owi ng pai r sofr eact ant s: ( a)2But anol andHBr ( b)1Tet r adecanol andHBr 3. I l l ust r at et hemechani sm f ort her eact i oni n2( a) . 52 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 4. 5React i onsofAl ky l Hal i des Al ky lhal i desdooneoft hef ol l owi ngt hi ngswhent heyr eactwi t hanucl eophi l eorabase suchasOH-:ei t hert heyunder gosubst i t ut i on,ort heyunder goel i mi nat i onofHXt oy i el san al kene. 4. 5. 1 Nucl eophi l i cSubst i t ut i onReact i ons React i oni nwhi cht hehal ogenat om i sr epl acedbyanucl eophi l e. Canbeusedt ot r ansf or m al ky l hal i desi nt oav ar i et yofot herf unct i onal gr oups. Ther ear et wocompet i ngmechani sms:SN1( Subst i t ut i onNucl eophi l i cUni mol ecul ar ) andSN2( Subst i t ut i onNucl eophi l i cBi mol ecul ar ) . A knowl edgeoft hef act or st hataf f ectsubst i t ut i onr eact i onshel pst odet er mi ne whi chr eact i onwi l lpr edomi nat e.Thedet er mi ni ngf act or si ncl udest r uct ur eoft he al ky lhal i de( t hesubst r at e) , st r engt hoft henucl eophi l e, nat ur eofsol v entandl eav i ng gr oupabi l i t y . Summar yoft heChar act ei si t i csofSN1andSN2React i ons I nf l uenci ngFact or SN2 SN1 Fav or s/ occur s at r el at i v el y Fav or ssubst r at eswhi chy i el dt he TheSubst r at e unhi nder ed si t es and usef ulonl y mostst abl ecar bocat i ons; bestf or wi t hCH3X,1o RXandaf ewsi mpl e 3o RX,as wel las al l y l i c and 2oRX. benzy l i chal i des. Nucl eophi l e may be negat i v el y Si nce SN1 r eact i on r at ei s not char ged or neut r al . Negat i v el y dependentont henucl eophi l e,t he char ged nucl eophi l es ar e usual l y nat ur eoft henucl eophi l epl ay sno mor er eact i v et han neut r alones. par t .Neut r alnucl eophi l esar ej us That ’ s why SN2 r eact i ons occur asef f ect i v easnegat i v el ychar ged mor eof t enunderbasi ccondi t i ons. nucl eophi l es. TheNucl eophi l e Nucl eophi l i t y usual l y i ncr eases downagr oupoft hePei odi cTabl e. Or derofNucl eophi l i ci t y :HS->HO-; I >Br >Cl TheLeav i ngGr oup Weaker bases ( conj ugat es of Si nce SN1 r eact i ons ar e car r i ed st r ong aci ds) ar e good l eav i ng out under aci di c condi t i ons, gr oups,whi l e st r ong bases ar e neut r alwat eract s as a l eav i ng poorl eav i nggr oups. gr oup. Rel at i v eReact i v i t yofNu:OR-,NH2-, Rel at i v eOr derofReact i v i t y :HO-< - - OH <F<Cl , Br, I , TsO.Ther ef or e, Cl<Br<I~TsO, H2O. al ky lf l uor i des,al cohol s,et her sand ami nes do not under go SN2 r eact i ons. TheSol v ent Pr ot i csol v ent sar ewor stf orSN2 St r ongl ypol arsol v ent s( wat erand r eact i ons( e. g.ROHor–NH-gr oup. met hanol )ar ev er ygoodf orSN1 Apr ot i csol v ent sar epol ar .Apr ot i c r eact i ons,whi l enonpol arsol v ent s sol v ent s i ncl ude: di met hy l( et herandchl or of or m)ar ewor st sul f oxi de ( DMSO) , di met hy lf orSN1r eact i ons. f or mami de( DMF) ,acet oni t r i l e,et c. ar e good sol v ent s f or SN2 r eact i ons. Ki net i cs 2nd Or der ( Rat e of r eact i on 1st Or der ( Rat e of r eact i on dependsonbot ht hesubst r at eand dependsonl yont hesubst r at e) 53 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 St er eochemi cal Out come t henucl eophi l e) I nv er si on of pr oduct conf i gur at i onof Ret ent i onofconf i gur at i onoft he pr oduct PRACTI CEPROBLEMS 1. Whatpr oductwoul dy ouexpectf r om SN2r eact i onof1br omobut anewi t heachoft he f ol l owi ng: ( a)NaI ( b)KOH 2. Whi chsubst r at ei neachoft hef ol l owi ngpai r si smor er eact i v easanucl eophi l e?Expl ai n. ( a)H2OorH2S ( b)( CH3) CH3) 3B OR( 3N 3. Rankt hef ol l owi ngcompoundsi nor deroft hei rexpect edr eact i v i t yt owar dSN2r eact i on: CH3Br ;CH3OTs; ( CH3) Cl ; ( CH3) HCl 3C 2C 4. Rankt hef ol l owi ngsubst r at esi nor deroft hei rexpect edSN1r eact i v i t y : 5. 3Br omo1but eneand1br omo2but eneunder goSN1r eact i onatnear l yt hesamer at eev en t houghonei s2ohal i deandt heot heri s1ohal i de.Expl ai n. 6. Pr edi ctwhet hereachoft hef ol l owi ngsubst i t ut i onr eact i onsi sl i kel yt obeSN1orSN2. 4. 5. 2 El i mi nat i onReact i ons I nanSN2r eact i on,a1o RXr eact swi t het hox i dei on.Howev er ,i fa3o RXr eact swi t h t hesamenucl eophi l e, anel i mi nat i onr eact i onoccur s. Mor ecompl ext hansubst i t ut i onr eact i ons. Pr oduct sar emi x t ur esofal kenes. El i mi nat i oni nv ol v i ngt hel ossof2gr oupsf r om adj acentcar bonat omsi scal l edβel i mi nat i on.St ongl ybasi cnucl eophi l espr omot eβel i mi nat i on. Zai t sev ’ sr ul e pr ov i des t hatbasedi nduced el i mi nat i on r eact i ons gener al l y( not al way s)gi v et hemor est abl eal kenepr oduct–t hati s,t heal kenewi t hmor eal ky l subst i t uent sont hedoubl ebondcar bons. Thr ee( 3)t y pesofel i mi nat i onmechani smsexi stexi st–E1,E2andE1cbcompet es wi t hSN1, whi l eE2compet eswi t hSN2. E2 -El i mi nat i on Bi mol ecul ar :i ti nv ol v est he r eact i on of3o al ky lhal i desi nt he o pr esenceofast r ongbase.I tcompet eswi t hSN2f or1 and2oRX. o Themechani sm i sasf ol l ows: o St r ongl ynegat i v el ychar gedbasesl i keOH-andOR-,aswel laspol arapr ot i c sol v ent sar epr ef er r edf orE2r eact i ons. 54 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 o Bet t ert hel eav i nggr oup, f ast ert her eact i on.RCl <RBr<RI o Or derofReact i v i t yofRX: 3oRX>2oRX>1oRX o I nsomecases,t hel essst abl eal kenebecomest hemaj orpr oductwhena hi nder edbasei susedwi t hahi nder edal ky l hal i de. E1-El i mi nat i onUni mol ecul ar :I ti sanal ogoust oSN1r eact i on.Themechani sm i sas f ol l ow: E1cB-El i mi nat i onUni mol ecul arConj ugat eBase:Occur st hr oughacar bani on( r at her t hanacar bocat i on)i nt er medi at e.I toccur swhent hel eav i nggr oupi s2car bonsaway f r om t hecar bony lgr oup.Ther eact i oni scommoni nsubst r at est hathav epoor l eav i nggr oups, suchas–OH.Poorl eav i nggr oupdoesnotf av orE1andE2. PRACTI CEPROBLEMS 1. Tel l whet hereachoft hef ol l owi ngr eact i onsi sl i kel yt obeSN1, SN2E1, E1cBorE2and pr edi ctt hepr oductofeach: 2. Tel l whet hereachoft hef ol l owi ngi sl i kel yt obeSN1, SN2E1, E1cBorE2: PROBLEM SETNO.4 1. Wr i t et hest r uct ur al f or mul asandgi v et hef unct i onal cl assandsubst i t ut i v enamesofal l i somer i cal ky l hal i dest hathav et hemol ecul arf or mul aC4H9Cl . 2. Gi v eI UPACnamesf ort hef ol l owi ngal ky l hal i des: 3. Dr awandnameal l monochl or opr oduct sy ouwoul dexpectt oobt ai nf r om t hef r eer adi cl chl or i nat i onof2met hy l pent ane. 4. Dr awst r uct ur escor r espondi ngt ot hef ol l owi ngI UPACnames: ( a)3, 3Di chl or o2met hy l hexane ( b)3Br omo3et hy l pent ane ( c)1, 1Di br omo4i sopr opy l cy cl ohexane( d)4secBut y l 2chl or ononane 5. Whatpr oduct swoul dy ouex pectf r om r eact i onof4, 4di met hy l cy cl ohex anewi t hNBS? 6. Whatpr oduct swoul dy ouex pectf r om t her eact i onoft hef ol l owi ngal keneswi t hNBS?I f mor et hanonepr oducti sf or med, showt hest r uct ur eofal l . 7. Howwoul dy oupr epar et hef ol l owi ngal ky l hal i desf r om t hecor r espondi ngal cohol s? 55 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 8. Wr i t eachemi cal equat i onf ort her eact i onbet ween3et hy l 3pent anol andHCl . 9. Gi v et hest r uct ur eoft hepr i nci pal or gani cpr oductf or medbyf r eer adi cal br omi nat i onof eachoft hef ol l owi ng: ( a)met hy l cy cl opent ane( b)1i sopr opy l 1mehy l cy cl opent ane( c)2, 2, 4t r i met hy l pent ane 10.Whatpr oductwoul dy ouexpectf r om t her eact i onof1chl or o1met hy l cy cl ohexanewi t hKOH i net hanol ? 11.I gnor i ngdoubl ebondst er eochemi st r y , whatpr oduct swoul dy ouexpectf r om el i mi nat i on r eact i onsoft hef ol l owi ngr eact i on?Whi chwi l l bet hemaj oror gani cpr oducti neachcase? 12.Whatal ky l hal i demi ghtt hef ol l owi ngal keneshav ebeenmadef r om? 13.Tel l whet hereachoft hef ol l owi ngi sl i kel yt obeSN1, SN2E1, E1cBorE2: TOPI C5: ALCOHOLS 5. 1I nt r oduct i onandCl assi f i cat i on 56 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Compoundst hathav ehy dr oxy lgr oups( OH)bondedt osat ur at edsp3hy br i di zedcar bon at oms. Maybeconsi der edasor gani cder i v at i v esofwat er( HOH)i nwhi choneHat om i sr epl aced byanal ky l gr oup( R) . Ther ef or e, al cohol sar egener al l ywr i t t enasROH. Cl assi f i cat i on:Pr i mar y( 1o) ,secondar y( 2o)ort er t i ar y( 3o)dependi ngont henumberof car bonat omsbear i ngt hehy dr oxy l ( OH)gr oup. 5. 2Nomencl at ur eofAl cohol s Whent heI UPACr ul esar eusedt onameanal cohol ,t hepar entchai n( l ongestcont i nuous car bonchai ncar r y i ngt he–OHgr oup)i snumber edf r om t heendnear ert he–OHandnamed bydr oppi ngt he“ e”endi ngont henameoft hecor r espondi nghy dr ocar bonbyaddi ng“ ol ” . Whenapar entchai ncont ai nsmor et han2car bonat oms,t heposi t i onoft he–OH gr oup mustbespeci f i edwi t hanumber . Anyal ky lgr oup/ subst i t uentat t achedt ot hepar entchai nar ei dent i f i edbyname, posi t i onand numberofappear ances. Somecommonnamesar eaccept edbyI UPAC. Hy dr oxy l gr oupt akespr ecedenceov eral ky l gr oupsandhal ogensubst i t uent s. PRACTI CEPROBLEMS 1. Dr awst r uct ur escor r espondi ngt ot hef ol l owi ngI UPACnames: ( a)( Z) 2Et hy l 2but en1ol ( b)3Cy cl ohexen1ol ( c)t r ans3Chl or ocy cl ohept anol( d)1, 4Pent anedi ol 2. Gi v et heI UPACnamesf ort hef ol l owi ngal cohol s: 57 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 5. 3Phy si cal Pr oper t i esofAl cohol s 5 Rel at i v el yhi gherboi l i ngpoi nt st hanhy dr ocar bonsofcompar abl emol ecul arwei ght sduet o abi l i t yt of or m hy dr ogenbonds 6 Low mol ecul arwei ghtal cohol s( met hy l ,et hy l ,npr opy l ,i sopr opy l )ar esol ubl ei nwat eri nal l pr opor t i ons.Thi si sl ar gel yduet ohy dr ogenbondi ng.Hi gheral cohol sar el esswat er sol ubl e.As t heal ky l chai nget sl ar ger , sol ubi l i t yi nwat erdecr eases. 7 Al ll i qui dal cohol shav edensi t i esofappr ox i mat el y0. 8g/ mLandar et her ef or el essdenset han wat er . 5. 4Sour cesandPr epar at i onofAl cohol s 8 Sour ces:Al cohol s occurwi del yi n nat ur e and hav e many i ndust r i aland phar maceut i cal appl i cat i ons. Met hanolusedt obepr epar edbyheat i ngwoodi nt heabsenceofai r ;hence,t he name ‘ wood al cohol ’ .Today ,i ti s manuf act ur ed on a l ar ge scal e bycat al y t i c r educt i onofcar bonmonoxi dewi t hhy dr ogengas.I t ’ susedasasol v entandasa st ar t i ngmat er i al f ort hepr oduct i onoff or mal dehy deandacet i caci d. Et hanolal sooccur swi del yi nnat ur e.I twasoneoft hef i r stor gani cchemi cal st obe pr epar ed. 9 Pr epar at i on:Al cohol soccupyacent r alposi t i oni nor gani cchemi st r ybecauset heycanbe pr epar edf r om manyot herki ndsofor gani ccompoundsj ustast heycanbet r ansf or medi nt oan equal l ywi dev ar i et yofor gani ccompounds.Manyoft hemet hodsofpr epar at i onofal cohol s hav ebenpr ev i ousl ydi scussed. Hy dr at i onofAl kenes:Anel ect r ophi l i caddi t i onr eact i on Oxy ner cur at i onDemer cur at i on:Anel ect r ophi l i caddi t i onr eact i on Hy dr obor at i onOxi dat i on: I t ’ s anot her al t er nat i v e f or hy dr at i on of al kenes. Regi osel ct i v i t yi sAnt i Mar kov ni kov ; st er eochemi st r yi ssy n. Reduct i onofAl dehy desandKet ones:Anucl eophi l i caddi t i onr eact i onoccur susual l y wi t hdi et hy let her( Et ort et r ahy dr of ur an( THF)assol v ent ,f ol l owedbyH3O+ wor k2O) 58 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 up. Reduct i onofCar boxy l i cAci dsandEst er s:Car boxy l i caci dsandedst er sar el ess r eact i v et onucl eophi l es.Hence,t hemor er eact i v er educi ngagent ,Li Al H4i sr equi r ed t han NaBH4 whi ch i sal so l essr eact i v e.Ther eact i on i sbot h nucl eophi l i cacy l subst i t ut i onandnucl eophi l i caddi t i on. PRACTI CEPROBLEMS 1. Whatcar bony l compoundswoul dy our educet oobt ai nt hef ol l owi ngal cohol s? 2. Whatr eagentwoul dy ouuset oaccompl i sheachoft hef ol l owi ngr eact i ons? 3. Whatcar bony lcompoundsgi v et hef ol l owi ngal cohol sonr educt i onwi t hLi Al H4? Showal l possi bi l i t i es. React i onofCar bony lCompoundswi t hGr i gnar dReagent s: RX + Mg RMgX Est er sr eactwi t h Gr i gnar dr eagent st oy i el d 3o al cohol si n whi ch t wo oft he subst i r ut ent sbondedt ot hehy dr oxy l bear i ngcar bonhav ecomef r om t heGr i gnar d 59 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 r eagent s, j ustasLi Al H4r educt i onofanest eraddst wo( 2)Hat oms. PRACTI CEPROBLEMS 1. Show t hepr oduct sf r om t headdi t i onofmet hy lmagnesi um br omi det ot he f ol l owi ngcar bony l compounds: 2. UseaGr i gnar dr eagentt opr epar et hef ol l owi ngal cohol s: ( a)2Met hy l 2pr opanol ( b)1Met hy l cy cl ohexanol ( c)3Met hy l 3pent anol ( d)4Met hy l 1pent anol 5. 5React i onsofAl cohol s 10 Conv er si ont oAl ky lHal i des: 11 Dehy dr at i onofAl cohol st oy i el dAl kenes: Reagenti s aqueous sul f ur i c aci di n THF sol v ent .Hence,t he r eact i on i s aci dcat al y zedandf ol l owsZai t sev ’ sr ul e. Wi t ht heuseofphosphor usoxy chl or i de,POCl npy r i di ne,dehy dr at i onof2o and3o 3i al cohol soccur . Sampl ePr obl em:Whatpr oduct ( s)woul dy ouexpectf r om t hedehy dr at i onoft he f ol l owi ngal cohol swi t hPOCl npy r i di ne?I ndi cat et hemaj orpr oducti neachcase. 3i 60 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 12 Conv er si onofAl cohol si nt oEst er s( Est er i f i cat i on) : 13 Oxi dat i onofAl cohol s( Mai nl y1oand2o) Oxi di zi ngagent si ncl ude: KMnO4, Cr O3andK2Cr Onasmal l scal e, al dehy sesar epr epar ed 2O7. f r om al cohol sbyoxi dat i onusi ngpy r i di ni um chl or ochr omat e( PCC) , C5H6NCr O3Cl i nCH2Cl 2. Pr act i cePr obl ems 1. Whatal cohol swoul dgi v et hef ol l owi ngpr oduct sonoxi dat i on? 2. Whatpr oduct swoul dy ouex pectf r om t heoxi dat i onoft hef ol l owi ngcompoundswi t hCr O3i n aqueousaci d?Wi t hPCC?( a)1Hexanol ( b)2Hexanol 61 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 TOPI C6: ALKENESSTRUCTURE, NOMENCLATURE, PHYSI CALPROPERTI ESANDPREPARATI ON 6. 1Descr i pt i onofAl kenes Al kenes( orol ef i ns)ar ehy dr ocar bonst hatcont ai n acar boncar bon doubl ebond.Thi s car boncar bondoubl ebondi st hechar act er i st i cf unct i onal gr oupf oral l al kenesandconsi st s ofoneσbondandoneπbond.Theyar eunsat ur at edhy dr ocar bons–t heycont ai nl esst han t hemaxi mum quant i t yofhy dr ogen. Gener al For mul a:CnH2n Someal kenesi ncl udeet hy l ene( usedf orr i peni ngoff r ui t s) ,αpi nene( acomponentof t ur pent i ne)andβcar ot ene( asour ceofv i t ami n) . 6. 2St r uct ur eofAl kenes Thesi mpl estal kenei set hy l eneoret hene, C2H4. Theov er l apoft hesp2 hy br i dor bi t al sf r om eachcar bonpr oducest heCCσbond,whi l et he si deway sov er l apoft heunhy br i di zedpor bi t alf r om eachcar bonf or mst heπbond.πbondi s weakert hanσbond.Consi derpr openef orex ampl e: Ther ear et wot y pesofCCbonds–t hedoubl ebondi sσ+πt y pe, whi l et hebondt ot he–CH3 i saσbondf or medbysp3sp2ov er l ap. Sampl ePr obl em: Fort heal kenebel ow: ( a)Wr i t et hemol ecul arf or mul a.( b)Howmanycar bonat omsar esp2hy br i di zedandhowmanyar e 3 2 3 sphy br i di zed?( c)Howmanyσbondsar eoft hespsp t y pe?( d)Howmanyar eoft hesp3sp3t y pe? 6. 3Nomencl at ur eofAl kenes Commonnamesar est i l lusedt odayf ort hr eesi mpl eal kenes:et hy l ene,pr opy l ene,and i sobut y l ene. Mostal kenesar enamedbyt heI UPACsy st em.Thef ol l owi ngr ul esar eappl i ed: Fi ndt hel ongestchai ncont ai ni ngt hedoubl ebondandnamet hecompound accor di ngl yusi ngt hesuf f i x–ene. 62 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Numbert hechai nf r om t heendnear estadoubl ebondcar bonat om sot hatt he car bonat omsoft hedoubl ebondgett hei rl owernumber s.Speci f yt hesmal l eroft he t wonumber s.Forexampl e, i nt heal kenegi v enabov e, t hedoubl ebondi sbet weenC1 andC2.Soi ti s1pent ene. NB. :Car boncar bondoubl ebondst akepr ecedenceov eral ky lgr oupsandhal ogensi n det er mi ni ngt hemai ncar bonchai nl engt handt hedi r ect i oni nwhi chi ti snumber ed. Howev er ,hy dr oxy lgr oups,OH,out r ank t he doubl e bond.I n such a case,t he combi nedsuf f i x–en+ol i sused. Wher et her ear emor et hanonesubst i t uent , l i stt hem al phabet i cal l y .I fmor et hanone doubl ebondi spr esent , i ndi cat et heposi t i onofeach, anduse–di ene, or–t r i ene, et c. Sampl ePr obl ems 1. Nameeachoft hef ol l owi ngusi ngI UPACnomencl at ur e: 2. Dr awt hest r uct ur al f or mul asf ort hef ol l owi ng: ( a)3Et hy l 5met hy l 3hept ene ( b)4t er t But y l 2met hy l 2hept ene ( c)2Met hy l 1, 5hexadi ene( d)1, 3, 5hexat r i ene 6. 4I somer i sm i nAl kenes I somer i sm exi st sf r om C4andabov ef oral kenes.Consi dera4car bonal kenef orexampl e; t hef ol l owi ngst r uct ur escanbedr awn: Onhy dr ogenat i onof2but eneandcl eav ageatt hedoubl ebond, i ti sf oundt hatt her ear et wo pr oduct s wi t h di f f er entphy si calpr oper t i es ( b. p. ,m. p. ,et c. ) .Unl i ke conf or mer s,t hese pr oduct sar enoti nt er conv er t i bl eduet ohi nder edr ot at i onaboutt hecar boncar bondoubl e 63 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 bond.Hence, t heycanbei sol at ed. Possi bl est r uct ur esoft het woi sol abl e2but enesar e: Ther ef or e,2but eneandmanyot herhi gheral kenesexhi bi tci st r ansi somer i sm,al soknown asgeomet r i ci somer i sm –t heex i st enceoft hesameconst i t ut i onali somer si nt wodi f f er ent spat i al ar r angement s( conf i gur at i ons) . Ci st r ansi somer i sm i nal kenesi snotpossi bl ewhenoneoft hedoubl ybondedcar bonsbear s t woi dent i cal subst i t uent s. Sampl ePr obl ems 1. Howmanyal keneshav et hemol ecul arf or mul aC5H10?Wr i t et hei rst r uct ur esandgi v et hei r I UPACnames.Speci f yt heconf i gur at i onasci sort r ans, appr opr i at el y . 2. Gi v et hest r uct ur al f or mul asf or : ( a)ci s2met hy l 3hept ene( b)t r ans2met hy l 1, 3pent adi ene. 3. Whi choft hef ol l owi ngcompoundscanexi staspai r sofci st r ansi somer s?Dr aweachci st r anspai r , andi ndi cat et hegeomet r yofeachi somer . ( a)CH3CH=CH2( b)( CH3) =CHCH3( c)CH3CH2CH=CHCH3( d)( CH3) =C( CH3) CH2CH3 ( e) 2C 2C Cl CH=CHCl( f )Br CH=CHCl 4. Gi v et heI UPACnameofeach; speci f yci st r ansconf i gur at i onwher enecessar y : Theci st r ansnami ngsy st em f ai l swi t ht r i subst i t ut edort et r asubst i t ut eddoubl ebonds.A mor egener almet hodf ordescr i bi ngdoubl ebondgeomet r yi spr ov i dedbyt heCahnI ngol dPr el og E/ Z sy st em ofnomencl at ur ewhi ch usesaser i esofsequencer ul est o assi gn pr i or i t i est ot hesubst i t uentgr oupsont hedoubl ebondcar bons.I ft hehi gherpr i or i t i esont he doubl ebondcar bonsar eont hesamesi de, wedesi gnat eZ( f orzusamen, aGer manwor df or “ t oget her ” ) .I ft hehi gherpr i or i t i esar eopposi t esi des,wedesi gnat eE ( f orent gegen,a Ger manwor df or“ opposi t e” ) . TheCahnI ngol dPr el ogr ul es( namedaf t erRober tS.Cahn,Si rChr i st opherK.I ngol dand Vl adi mi rPr el og)ar easf ol l ows: 64 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Consi der i ngeachoft hedoubl ebondcar bonssepar at el y ,i dent i f yt het woat oms di r ect l yat t achedandr ankt hem accor di ngt oat omi cnumber .Hi gherat omi cnumber get shi gherpr i or i t y . Or derofpr i or i t yofat om at t achedt odoubl ebond:Br >Cl >F>O>N>C>H I fadeci si oncannotber eachedbyr anki ngt hef i r stat omsi nt hesubst i t uent , l ookat nd r d t h t he2 , 3, or4 at om awayf r om t hedoubl ebondcar bonsunt i l t hef i r stdi f f er encei s f ound.Forex ampl e, CH2CH3>CH3becauset he2ndat om ofet hy l i sacar bon, whi l e t he2ndat om ofmet hy l i sahy dr ogen. Mul t i pl ebondedat omsar eequi v al entt ot hesamenumberofsi ngl ebondedat oms. Forexampl e, CH=Oequi v al entt o Ot herequi v al entpai r si ncl ude: Exampl es: Sampl ePr obl ems 1. Gi v et heI UPACnameofeach, speci f y i ngE/ Zconf i gur at i onappr opr i at el y : 65 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2. Dr awst r uct ur al f or mul asf or : ( a)( E) 2chl or o2but ene( b)( Z) 1, 4hex adi ene ( c)( Z) 1chl or o2cy cl opent y l 1pent ene( d)( E) 2, 4di met hy l 1pent en1ol ( e)( Z) 1br omo3met hoxy 2, 5di met hy l 3hex ene 6. 5Phy si cal Pr oper t i esofAl kenes Al kenesr esembl eal kanesi nmostoft hei rphy si cal pr oper t i es. Lowermol ecul arwei ghtal kenesupt oC4ar egasesatr oom t emper at ur eandat mospher i c pr essur e. I nsol ubl ei nwat er , butqui t esol ubl ei nnonpol arsol v ent sl i kebenz ene, et her , chl or of or m or l i gr oi n. Lessdenset hanwat er . Boi l i ngpoi ntr i seswi t hi ncr easi ngcar bonnumber . 6. 6Rel at i v eSt abi l i t i esofAl kenes Ci sal kenesar el essst abl et hant hei rt r ansi somerbecauseofst er i c( spat i al )hi ndr ance st r ai nbet weent het wobul kysubst i t uent sont hesamesi deoft hedoubl ebond.I fwe i nt er conv er tci s2but enebyt r eat mentwi t hast r ongaci dcat al y standal l ow t hem t or each equi l i br i um, wef i ndt hatt het r ansi s76%, whi l et heci si s24%.∆G=2. 8kJ/ molhi gherf ort he ci si somer . Heat sofcombust i onmeasur ement sshowt hatci si someri smor est r ai nedby3. 3kJ/ mol . Heat sofhy dr ogenat i onmeasur ement sal soshow t hatt heci si smor eunst abl et hant he t r ansasmor eheati sr el easedonhy dr ogenat i on. Al kenesbecomemor est abl ewi t hi ncr easi ngsubst i t ut i on.Al kenesf ol l owt hest abi l i t yor der : R2C=CR2>R2C=CHR>RCH=CHR>R2C=CH2>RCH=CH2.Ther easonsf orsai dobser v edst abi l i t y ofal kenesar edegr eeofsubst i t ut i on, VanderWaal ’ sst r ai nandbondst r engt h. Sampl ePr obl ems 1. Whi chal kenei neachoft hef ol l owi ngset si smor est abl e?( a)1But eneor2met hy l pr opene ( b)( Z) 2Hexeneor( E) 2hex ene 2. Ar r anget hef ol l owi ngal kenesi nor derofdecr easi ngst abi l i t y : 1pent ene; ( E) 2pent ene; ( Z) 2pent ene; 2met hy l 2but ene . 6. 7Sour cesandPr epar at i onofAl kenes Al kenesar eobt ai nedi ndust r i al l ybycr acki ngofpet r ol eum.Smal l eral kenescanbeobt ai ned i npur ef or m byf r act i onaldi st i l l at i onandar et husav ai l abl ef orconv er si oni nt ol ar genumber ofal i phat i ccompounds. Et hy l eneandpr opy l enear et het womosti mpor t antor gani cchemi cal spr oducedi ndust r i al l y . Byt het her mal cr acki ngofnat ur al gasandgasol i ne, t hel oweral kenes( C1C4)ar eobt ai ned. 66 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Pur esampl esofmor ecompl i cat edal kenesmustbepr epar edi nt hel abor at or y .Al kene pr epar at i onr equi r esanel i mi nat i onr eact i onj ustl i ket heel i mi nat i onofhy dr ogeni nt he pr ocessofdehy dr ogenat i on. Theel i mi nat i onr eact i oni nv ol v edi nt hef or mat i onofanal kenei saβel i mi nat i on, al soknown as1, 2el i mi nat i on.Cr acki ngwhi chi sal soadehy dr ogenat i onr eact i oni saβel i mi nat i on r eact i on, buti ti snotapr act i cal l abor at or ymet hodf ormostal kenes. Thef ol l owi ngar et hepr i nci pal βel i mi nat i onmet hodsf orpr epar i ngal kenesi nt hel ab. 1. Dehy dr ohal ogenat i onofal ky lhal i des( RX) :Ast r ongbase,usual l yKOH orNaOC2H5i s r equi r ed;met hanol ,et hanolorDMSO( di met hy lsul f oxi de)i susedasasol v ent .NaOEt wor kswi t hmet hanol , whi l eKOHwor kswi t het hanol orDMSO.Pot assi um t er t but oxi dei s o t hepr ef er r edbasewhen1 RXi sused,andi nt hi scaset er t but y lal coholorDMSOi s usedasasol v ent . Al so,dehy dr ohal ogenat i on i sr egi osel ect i v e;i tf ol l ows t he Zai t sev r ul e:βel i mi nat i on pr edomi nat esi nt hedi r ect i ont hatl eadst ot hemor ehi ghl ysubst i t ut edal kene( i . e. ,al kene f or medi nt hegr eat estamounti st heonet hatcor r espondst ot her emov aloft hehy dr ogen f r om t heβcar bonhav i ngt hef ewesthy dr ogen.Al so, dehy dr ohal ogenat i oni sst er eosel ect i v e, f av or i ngt hef or mat i onoft hemor est abl est er eoi somer , t r ans( orE) . 67 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 EaseofDehy dr ohal ogenat i on:3o>2o>1o. React i onMechani sm ( a)E2Mechani sm:Pr oposedi n1920bySi rChr i st opherI ngol d.Her ef er r edt ot hi sasE2 ( el i mi nat i onbi mol ecul ar )basedont hef actt hatt heov er al lr eact i onshows2nd or der st ki net i cs( f i r stor deri nt heal ky lhal i deand1 or deri nt hebase) , andal sot hatt her at eof el i mi nat i on dependson t hehal ogen ( t her eact i v i t yofal ky lhal i desi ncr easeswi t h decr easi ngst r engt hofCXbond) . Or derofReact i v i t y :RF<RCl <RBr <RI Thi smeansIi st hebestl eav i nggr oup. TheE2mechani sm i sasi ngl est epmechani sm, buti nv ol v est hr eekeycomponent s: ( i )CH bondbr eaki ngwi t ht hef or mat i onofabondbet weenH+andt heOH-oft hest r ongbase; ( i i ) C=Cπbondf or mat i on; and( i i i )CXbondbr eaki ngbysal v at i on. ( b)E1Mechani sm:I ti sE1( el i mi nat i onuni mol ecul ar )becausei texhi bi t s1stor derki net i csi nwhi ch t her at edet er mi ni ngst epi nv ol v esonl yt heal ky lhal i deandnott hebase.I ti st y pi calof3oandsome 2o al ky lhal i des,andt henonl ywhent hebasei sweakorl ow i nconcent r at i on. Rat eor derof el i mi nat i onbyE1Mechani sm i s1o RX<2o RX<3o RX.Ther ef or e,3o RXhast hef ast estr at eofE1 el i mi nat i on, whi l e1oRXpr ef ert heE2el i mi nat i on. Ther ear et wo( 2)st epsi nE1mechani sm: St ep1:I oni zat i onorhet er ol y t i ccl eav ageoft heRX. St ep2:Depr ot onat i onbyt hesol v entwhi chact sasabaset or emov eH+f r om t hecar bocat i on( R+)t o gi v et heal kenepr oduct s. Fort her eact i on: 68 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Theabov er eact i oni sE1mechani sm becauset hi si sa3oRX Thebestexampl esofE1el i mi nat i onsar et hosecar r i edouti nt heabsenceofaddedbase; i n suchacase, t hebasecoul dbet hesol v entmol ecul easseeni nt hepr ev i ousexampl e.I nE1, car bocat i onmayr ear r angef r om al essst abl et o amor est abl ef or m.Thest abi l i t yof car bocat i oni soft heor der :3o>2o>1o>CH3+.E2el i mi nat i onr equi r esnor ear r angement . Sampl ePr obl ems 1. Gi v est r uct ur esofal lal kenesexpect edf r om dehy dr ohal ogenat i onoft hef ol l owi ngal ky l hal i des.Appl yt heZai t sevr ul et opr edi ctt heal kenef or medi nt hegr eat est / gr eat eramounti n eachcase:( a)1chl or opent ane( b)t but y lchl or i de( c)3br omo3et hy l pent ane( d)2chl or o2, 3di met hy l but ane 2. What al ky lhal i de ( i f any ) woul dy i el d each of t he f ol l owi ng pur e al kanes upon dehy dr ohal ogenat i on?( a)I sobut y l ene( b)2Pent ene( c)2Met hy l 1but ene( d)2Met hy l 2but ene( e)3Met hy l 1but ene 3. Wr i t est r uct ur alf or mul asf oral lt heal kenest hatcanbef or med i nt her eact i onof2br omobut anewi t hpot assi um et hoxi de. 2.Dehal ogenat i onofv i ci nal di hal i des Thi st y peofr eact i oni susedt or egener at eanal kenewhent her ei sanoper at i on( r eact i on)t o beper f or medonanot herpar toft heal kenemol ecul e.I nsuchacase,t heal kene( doubl e bond)i spr ot ect edbybei ngconv er t edt ot hedi hal i de,andt hent hesamedi hal i dei susedt o r egener at et heal kene. 69 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 3.Dehy dr at i onofAl cohol s Al cohol sar ecompoundswhi chcont ai nanal ky lgr oupandahy dr oxy lgr oup,OH.I nt he conv er si onofanal coholt oal kene, t her ei saβel i mi nat i onofamol ecul eofwat erbyt hel oss oft heHandOHf r om adj acentcar bons.Dehy dr at i onr equi r est hepr esenceofanaci dand t he appl i cat i onofheat . 2o Al cohol sunder goel i mi nat i onatl owert emper at ur est han1o al cohol s,and3o al cohol sat o o o o l owert emper at ur est han2 al cohol s.Ther ef or e, easeofdehy dr at i on: 3>2>1 Li kedehy dr ohal ogenat i onofaky lhal i des,dehy dr at i onofanal coholf ol l owst heZai t sevr ul e. Hence, t hemosthi ghl ysubst i t ut edal kenei spr ef er r ed.Ther eact i oni sal sost er eosel ect i v e. Usual l y , t hemor est abl et r ansst er eoi somerpr edomi nat es. Exampl es: 70 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 React i onMechani sm For3oand2oal cohol s, t hedehy dr at i onmechani sm i sE1i nv ol v i ngt hr ee( 3)st eps: i . Pr ot onat i onoft heal cohol : i i . Di ssoci at i onoft heal ky l oxoni um i ont of or mt hecar bocat i on: i i i . Depr ot onat i onoft hecar bocat i ont opr oducet heal kene: For1oal cohol s, i ti sbel i ev edt hatapr ot oni sl ostf r om t heal ky l oxoni um i oni nt hesamest ep i n whi ch car bonox y gen bond cl eav age t akes pl ace.Hence,t he r at edet er mi ni ng st ep i nv ol v est womol ecul es.Ther ef or e, i ti sel i mi nat i onbi mol ecul ar , E2. Lessst abl ecar bocat i onsr ear r anget omor est abl ecar bocat i onsbymet hy lorhy dr i deshi f t . Onceconv er t edt ot hecor r espondi ngcar bocat i on,t hatcar bocat i on,R+,coul dl oseapr ot on t ogi v eanal kenehav i ngt hesamecar bonskel et onorr ear r anget oadi f f er entcar bocat i on. Theor derofst abi l i t yofcar bocat i oni s: 3o>2o>1o. Exampl es: 71 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 2.Reduct i onofAl ky nes( TOBEDI SCUSSED) Sampl ePr obl ems 1. I dent i f yt heal keneobt ai nedondehy dr at i onofeachoft hef ol l owi ngal cohol s: ( a)3Et hy l 3pent anol ( b)I sopr opanol( c)nPr opanol( d)2, 3, 3t r i met hy l 2but anol 2. Baseont heZai t sevr ul e, pr edi ctt hemaj orpr oductofdehy dr at i onofeachoft hef ol l owi ng: ( a)( CH3) ( OH) CH2CH3 ( b)( CH3) HCH( OH) CH3( C)( CH3) ( OH) CH( CH3) 2C 2C 2C 2 3. Whatt hr eeal kenesar ef or medi nt heaci dcat al y zeddehy dr at i onof2pent anol .Showt he mechani sm i nv ol v ed. 6. 8Cy cl oal kenes 6. 8. 1Nomencl at ur e Cy cl i cal kenesar enamedi nexact l yt hesamewayast hei racy cl i ccount er par t s,ex ceptt hat t hedoubl ebondi nt hecy cl oal kenesoccupi esposi t i ons1and2.So,t her e’ snoneedt o i ndi cat et hi snumberwhenwr i t i ngt hename,butt hef i r stsubst i t uentmusthav easl ow a numberaspossi bl e. Exampl es: 72 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 73 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 CHAPTER7: REACTI ONSOFALKENES 7. 1Cl assi f i cat i onofAl keneReact i ons Gener al l yspeaki ng,al kenesunder gor eact i onswhi chcanbecat egor i zedasaddi t i on,subst i t ut i on andoxi dat i on.Thechar act er i st i cr eact i onofal kenesi saddi t i ont ot hecar boncar bondoubl ebond. Bei ng el ect r onr i ch,t he car boncar bon doubl e bond r eact s wi t h el ect r ophi l es.Hence,al kenes under goel ect r ophi l i caddi t i on. Addi t i onr eact i onst oal kenesmaybest er eosel ect i v e.Ther emaybesy norsupr af aci aladdi t i on ( wher et henew bondsar ef or medont hesamesi de/ f aceoft hedoubl ebond) ,orant iaddi t i on ( ant ar af aci aladdi t i on)i nwhi cht henew bondsar ef or medonopposi t esi desoft hedoubl ebond. Al so, t headdi t i onr eact i onsmayber egi osel ect i v ewhent heel ect r ophi l eaddst oanunsy mmet r i cal l y subst i t ut eddoubl ebond. Al kenesal sounder gof r eer adi cal addi t i on. 7. 1. 1Addi t i onReact i ons 1. Cat al y t i cHy dr ogenat i on: Hy dr ogenat i oni sar educt i onaddi t i onr eact i on.Themet al cat al y st si ncl udePt , Pd, Ni , Rh. 74 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Heat sofhy dr ogenat i onar eusedt ocompar er el at i v est abi l i t i esofal kenes. Sol v ent susedf orhy dr ogenat i onr eact i onsi ncl udeet hanol ,hexaneandacet i caci d–sel ect i v i t yi s basedoni t sabi l i t yt odi ssol v et heal kene. Mechani sm:1st, H2i sadsor bedatt hesur f aceoft hemet alcat al y st .Next , H2( t woat oms)i si nser t ed andt hecat al y sti sdi schar ged. 2. El ect r ophi l i cAddi t i on ( a)Addi t i onofHal ogens Sol v ent si ncl ude: acet i caci d, CCl CHCl ndCH2Cl React i onoccur satr oom t emp. 4, 3a 2. 75 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Hal ogenat i oni sst er eosel ect i v e. Tr ans2but enegi v esonl ymeso2, 3di br omobut ane.Ther eact i onofCl ndBr sanant i addi t i on. 2a 2i ( b)Addi t i onofHy dr ogenHal i desandSul f ur i cAci d 76 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Or derofr eact i v i t y :HF<<HCl <HBr <HI ;HXr eact sasagas;al kenemaybegasorl i qui d.HFi st he sl owest r eact i ng,meani ngt hel eastaci di c;HIi st hef ast est r eact i ng,meani ngt hemostaci di c.For HX, sui t abl esol v ent si ncl udepent ane, benzene, di chl or omet hane, chl or of or m andacet i caci d. Mechani sm El ect r ophi l i caddi t i onaddi t i onofHXt oal kenespr oceedsbyt her at edet er mi ni ngf or mat i onofa car bocat i oni nt er medi at e. Forsy mmet r i calal kenes,onl yonepr oducti spossi bl ef r om t headdi t i onofHX.Howev er ,f or unsy mmet r i calal kenes( subst i t ut edornot ) ,hy dr ogenaddst ot hecar bont hathast hegr eat er numberofhy dr ogensubst i t uent s.Thi si st heMar kov ni kov ’ sr ul e. 77 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 I nt headdi t i onofHXt oal kenes, pr ot onat i onoft hedoubl ebondoccur si nt hedi r ect i ont hatgi v est he mor est abl eoft wopossi bl ecar bocat i ons.Usi ngexampl e( i ) , weget : Or deroff or mat i on/ st abi l i t yofcar bocat i on: 3o>2o>1o Car bocat i onr ear r angementmayoccurv i aa1, 2-al ky l orhy dr i deshi f t . Fr eeRadi cal Addi t i onofHBrt oAl kenes–ThePer oxi deEf f ect HBrf ol l owst heMar kov ni kov ’ sr ul eonl yi fbot ht heal keneandHBrar epur e.I ft heHBrcont ai ns t r acesofor gani cper oxi des( ROOR)asi mpur i t i es( usual l yar i si ngf r om t hesl owr eact i onofO2f r om t heai rwi t hal kenes) ,t her eact i onbecomesant i Mar kov ni kov– t hecondi t i onr ef er r edt oast he 78 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 per oxi deef f ect .Onl yHBrf ol l owsbot hcar bocat i onandf r eer adi calmechani sms.HClandHIf ol l ow onl yt hecar bocat i onmechani sm whi chf ol l owst heMar kov ni kov ’ sr ul e. Addi t i onofH2SO4 Byheat i ngt hepr oductabov ewi t hwat erorst eam, anal cohol i spr oduced. ( c)Conv er si onofAl kenest oVi ci nal Hal ohy dr i ns Ahal ohy dr i ni sa1, 2hal oal coholandi sf or medwhenanal keneaddsi ndi r ect l yt oHOClorHOBrv i a ahal ogen( Br rCl nt hepr esenceofwat er .Ther eact i oni sant iasHO-and–Xaddt oopposi t e 2o 2)i f acesoft hedoubl ebond,andr egi osel ect i v eas–OHaddst ot hemor ehi ghl ysubst i t ut edcar bonof t hedoubl ebond. Mechani sm 79 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 I npr act i ce,f ew al kenesar esol ubl ei nwat er ,andbr omohy dr i nf or mat i oni sof t encar r i edouti na sol v entsuchasaqueousDMSO,usi ngar eagentcal l edNbr omosucci nami de( NBS)asasour ceof Br Si sst abl e,easi l yhandl edcompoundt hatsl owl ydecomposesi nwat ert oy i el dBr ta 2.NB 2a cont r ol l edr at e.Br omi nei t sel fi sdanger ousandmor edi f f i cul tt ohandl e. ( d)Aci dCat al y zedHy dr at i onofAl kenes Wat eraddst oal kenest oy i el dal cohol s,apr ocesscal l edhy dr at i on.Aqueousdi l ut eaci ds( 50% H2O/ H2SO4)cat al y zet her eact i on. Mar kov ni kov ’ sRul e 80 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Mechani sm ( e)Oxy mer cur at i onDemer cur at i on Mechani sm 81 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 ( f )Hy dr obor at i onOxi dat i on I nt hi sr eact i on,abor onhy dr i de,R2BH,addst oanal kenet oy i el danor ganobor anei nt er medi at e, RBH2orR2BHwhi chupont r eat mentwi t hH2O2i naqueousbasey i el dsanal cohol . 82 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 ( g)Addi t i onofCar benes Car benei sader i v at i v eofmet hy l ene.Met hy l enei sf or medbyt hephot ol y si sofdi azomet hane, CH2N2 orket ene, CH2=C=O. ( h)Di mer i zat i onandPol y mer i zat i on Underpr opercondi t i ons,2met hy l pr opene,C4H8,i sconv er t edbyconcent r at edsul f ur i caci dand phosphor i caci di nt oami xt ur eoft woal kenesofmol ecul arf or mul a,C8H16.Ther ef or e,C8H16 i sa di merofC4H8. ( t hemonomer )andt her eact i oni sknownasaci dcat al y zeddi mer i zat i on. Ther eact i onoccur swi t hMar kov ni kovr egi ospeci f i ci t yt ogi v eaR3C+.Thel esssubst i t ut edal kenei s t hemaj orpr oduct . I nsomecases,r eact i oncondi t i onscanbedesi gnedt of av ort hef or mat i onofhi ghermol ecul ar wei ghtpol y mer s.[ NB.Readoncat i oni cpol y mer i zat i onandf r eer adi cal pol y mer i zat i on. ] ( i ) Al ky l at i onofAl kenes: Theaddi t i onofanal kenet oanal kene, cat al y z edbyaci d. 83 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 7. 1. 2 Subst i t ut i onReact i on Hal ogenat i onofanal kenecanbecar r i edoutundercondi t i onsunf av or abl ef ort headdi t i onoft he hal ogenst obot hcar bonsoft hedoubl ebond( i . e. ,t hei oni cr eact i on) .Suchcondi t i onspr ev ai lata hi gh t emper at ur e of500600oC orl ow concent r at i on ofhal ogen and do f av ora f r eer adi cal subst i t ut i onr eact i on. Subst i t ut i onoccur satt heal l y l i ccar bon( t hecar bonnextt ot hedoubl ebond)–hence,t hi si sal so cal l edal l y l i csubst i t ut i on.Nbr omosucci nami de( NBS)speci f i cal l ybr omi nat esatt heal l y l i ccar bon. 7. 1. 3 Oxi dat i onReact i ons Oxi dat i onr eact i onsofal kenesi ncl udeepoxi dat i on, hy dr oxy l at i onandcl eav age. 1. Epoxi dat i on–t hef or mat i onofepoxi des( t hr eemember edr i ngst hatcont ai noxy gen) . Epoxi desar eal socal l edoxi r anesandwer eoncecal l edoxi desofal kenes.Epoxi dat i oni s t her eact i onofanal kenewi t haper oxyaci dt of or m anepox i de. 84 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 85 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 TOPI C8: STEREOCHEMI STRY St er eochemi st r yi st hatsubdi sci pl i neofor gani cchemi st r yt hati sdev ot edt ot hest udyof or gani cmol ecul esi nt hr eedi mensi ons.Compoundswhi chdi f f eri n3Dst r uct ur est hatar e noti nt er changeabl e,buthav et hesameat omsbondedbyt hesamesequenceofbondsar e t er medst er eoi somer s.The3D st r uct ur esar ecal l edconf i gur at i ons.The3D shapeofan or gani cmol ecul ecanhav eadr amat i cef f ectuponi t sr eact i v i t y .St er eochemi st r yi sder i v ed f r om t heGr eekwor d“ st er eos”meani ng“ sol i d” . 8. 1Rev i ewandOv er v i ewofI somer i sm Compounds t hatdi f f eri nt hei rphy si caland chemi calpr oper t i es,buthav et he same mol ecul arf or mul aar ecal l edi somer s.Thet y pesofi somer i sm ar est r uct ur al / const i t ut i onal i somer i sm andst er eoi somer i sm. 8. 1. 1 Di f f er encesBet weenConst i t ut i onal I somer i sm andSt er eoi somer i sm Const i t ut i onal I somer i sm St er eoi somer i sm 1.Compoundshav et hesamemol ecul ar Compounds hav et he same mol ecul ar f or mul abutdi f f erf r om eachot herby f or mul a and st r uct ur e, but di f f er i n hav i ngdi f f er entst r uct ur es. geomet r y / conf i gur at i on ( spat i al ar r angement ) . 2.At omsar econnect eddi f f er ent l y . At omsar econnect edi nt hesameor der . 3.I UPACnamesar edi f f er ent . I UPACnamesar et hesame. 4.Fur t hersubdi v i dedi nt ochai n Fur t hersubdi v i dedi nt oconf or mat i onal i somer i sm, f unct i onal gr oupi somer i sm st er eoi somer i sm andconf i gur at i on andposi t i onal i somer i sm. i somer i sm. Conf i gur at i oni somer i sm i sst i l l f ur t hersubdi v i dedi nt oopt i cal i somer i sm andgeomet r i c( ci s t r ans) i somer i sm.Agai n opt i cali somer i sm can be cl assi f i ed as enant i omer s and di ast er eomer s. 8. 1. 2Def i ni t i ons/ Descr i pt i ons Chai ni somer i sm: I somer sdi f f eri nt hev ar i at i onoft hecar bonchai norskel et onof t hemol ecul e.E. g.nBut aneandI sobut ane Funct i onal gr oupi somer i sm: I somer sdi f f eri nt het y peoff unct i onal gr ouppr esent . Eg.Et hy l al cohol andDi met hy l et her ; Pr opi oni caci dandmet hy l acet at e Posi t i onal i somer i sm: I somer sdi f f eri nt heat t achmentoft hesamef unct i onal gr oup t ot hechai ni ndi f f er entposi t i ons.E. g.Pr opanol andi sopr opanol Conf or mat i onal st er eoi somer s( conf or mer s) : Theydi f f eronl ybecauseofr ot at i on aboutsi ngl ebonds.Toi nt er conv er t , nocov al entbondsar er upt ur ed. Conf i gur at i onst er eoi somer s: Theydi f f eri nspat i al ar r angement . Enant i omer s: Mi r r or i magei somer s. Di ast er eomer s: Nonmi r r or i magei somer s Geomet r i ci somer s: Ci st r ansi somer s. 8. 2Enant i omer i sm andMol ecul arChi r al i t y Enant i omer i sm i st heexi st enceofi somer swhosest r uct ur esdi f f eronl yi nbei ngmi r r ori magesof 86 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 eachot her .Thecr edi tf ort hedi scov er yofenant i omer i sm goest ot heFr enchchemi st , Loui sPast eur . Past eurhadwor kedont hecr y st al l i nesal t soft ar t ar i caci dder i v edf r om wi neandhadobt ai nedt wo di st i nctki ndsofcr y st al suponcr y st al l i zat i onofaconcent r at edsol ut i onofsodi um ammoni um t ar t ar at ebel ow28oC. Ev er y t hi nghasami r r ori mage, butnotal lt hi ngsar esuper i mposabl eont hei rmi r r ori mages. Forexampl e,achai ri ssuper i mposabl eoni t smi r r ori mage,whi l ehandsar enot .Si mi l ar l y , cer t ai nmol ecul esar esuper i mposabl eont hei rmi r r ori mages, whi l eot her sar enot .Apai rof st er eoi somer s whi ch ar e noni dent i cal ,nonsuper i mposabl e mi r r ori mages ar e cal l ed enant i omer s. Consi dert hef ol l owi ngexampl es: Mol ecul est hatar enotsuper i mposabl eont hei rmi r r ori magesar echi r al( der i v edf r om t he Gr eekwor d,“ chei r ” ,meani ng“ hand” .Hence,mol ecul espossessi ngchi r al i t yar esai dt o possess“ handedness” .Acompoundwhosemol ecul esar echi r alcanexi stasenant i omer s. A mol ecul et hati ssuper i mposabl eoni t smi r r ori magei sachi r al( wi t houtchi r al i t y )and cannotexi stasenant i omer s. At et r ahedr alcar bont hatbear sf ourdi f f er entsubst i t uent si sr ef er r edt oasachi r alcent er , ot her wi ser ef er r edt oasasy mmet r i ccent erorasy mmet r i ccar bonorst er eogeni ccent er . 87 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Sampl ePr obl ems 1. I dent i f yt hest er eogeni ccent er s, i fany , i n: ( a)2br omopent ane( b)3br omopent ane( c)1br omo2met hy l but ane( d)2br omo2met hy l but ane( e)2cy cl opent en1ol ( f )3cy cl opent en1ol ( g)1, 1, 2t r i met hy l cy cl obut ane( h)1, 1, 3t r i met hy l cy cl obut ane 2. Whi choft hef ol l owi ngar echi r al ?( a)Ascr ewdr i v er( b)Ashoe( c)Ahammer 3. Pl aceast er i cksatal l st er eogeni ccent er si nt hef ol l owi ngmol ecul es: 8. 3Pr oper t i esofChi r al Mol ecul es 8. 3. 1Opt i cal Act i v i t yandSpeci f i cRot at i on Onepr oper t y( aphy si cal pr oper t y )ofchi r al mol ecul esi st hatt heyar eopt i cal l yact i v e.Opt i cal act i v i t yi st heabi l i t yofasubst ancet or ot at et hepl aneofapl anepol ar i zedl i ght .Whena beam ofor di nar yl i ghti spassedt hr oughadev i cecal l edapol ar i zer ,onl yt hel i ghtwav es osci l l at i ngi nasi ngl epl anepasst hr ough–hence, t hel i ghti spl anepol ar i zed.Li ghtwav esi n al lot herpl anesar eusual l yani nf i ni t enumberofpl anesatr i ghtangl est ot hedi r ect i onof l i ghtt r av elmakeupt hebeam ofor di nar yl i ghtwav es.Enant i omer sr ot at epl anepol ar i zed l i ghti nopposi t eway s, butequal i nmagni t ude. Opt i calact i v i t yi sdet ect edandmeasur edi nt er msoft heamountofr ot at i onbyusi ngan i nst r umentknownasapol ar i met er .Theamountofr ot at i oni ssi mpl yt henumberofdegr ees t hatwemustr ot at et hel enst oconf or m wi t ht hel i ght .Amountofr ot at i oni sdesi gnat edasα, whi l edi r ect i onofr ot at i oni sdesi gnat edas+or–( +f orr i ght / cl ockwi ser ot at i onand–f or 88 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 l ef t / count er cl ockwi ser ot at i on) .I ft her ot at i oncausedbyt heenant i omeri scl ockwi se,i ti s dext r or ot ar y( d) ; i ft her ot at i oni scount er cl ockwi se, t heenant i omeri sl ev or ot ar y( l ) . Si ncet heamountofr ot at i onobser v edi napol ar i met eri si nf l uencedbyt henumberof opt i cal l yact i v emol ecul es( t hati s, sampl econcent r at i on)andt hel engt hoft hesampl et ube, opt i calact i v i t yi smeasur edi nt er msofspeci f i cr ot at i on.Speci f i cr ot at i oni sdef i nedast he numberofdegr eesofr ot at i onobser v edi fadeci met ert ubei sused, andt hecompoundbei ng exami nedi spr esentt ot heext entof1g/ cm3.Theamountofwav el engt husedi s589nm ( r ef er r edt oassodi um Dl i ne) . li smeasur edi ndm ( 1dm =10cm) ; concent r at i oni smeasur edi nuni t sofg/ mL; speci f i cr ot at i on, α i smeasur edi ndegr ees.D=589nm l i ghtf r om aNal amp. 8. 3. 2Racemi zat i onandResol ut i on Tobeopt i cal l yact i v e, t hesampl emustcont ai nachi r alsubst anceandoneenant i omermust bepr esenti nex cessoft heot her .A sol ut i oncont ai ni ngequalamount sofenant i omer s t her ef or eexhi bi t snonetr ot at i on.Mi xt ur escont ai ni ngequalamount sofenant i omer sar e cal l edr acemi cmi xt ur es.Racemi xmi xt ur esar eopt i cal l yi nact i v e.Att hel i mi t ,wher eal lt he mol ecul es ar e oft he same handedness ( t hati s,a col l ect i on cont ai ni ng onl y one eneat i omer i cf or m) , wesayt hesubst ancei sopt i cal l ypur eorenant i opur e. Opt i cal pur i t y=per centenant i omer i cex cess=%ofoneenant i omer-%oft heot her Ther ef or e,A50% opt i cal l ypur esampl econt ai ns75% ofoneenant i omerand25% oft he ot her . Apr ocesswher ebyenant i omer sar esepar at edi scal l edar esol ut i on.Thet r ansf or mat i onofa pur eenant i omeri nt oi t sr acemat ei scal l edr acemi zat i on. Sampl ePr obl ems 1. Theconcent r at i onofchol est er oldi ssol v edi nchl or of or mi s6. 15gper100mLofsol ut i on. ( a)Apor t i onoft hi ssol ut i oni na5cm pol ar i met ert ubecausesanobser v edr ot at i onof1. 2.Cal cul at et hespeci f i cr ot at i onofchol est er ol .( b)Pr edi ctt heobser v edr ot at i oni f 10mLoft hesol ut i onwer edi l ut edt o20mLandpl acedi na5cm t ube. 2. Asampl eofsy nt het i cchol est er olwaspr epar edconsi st i ngent i r el yoft heenant i omerof nat ur alchol est er ol .Ami x t ur eofnat ur alandsy nt het i cchol est er olhasaspeci f i cr ot at i on of13.Whatf r act i onoft hemi xt ur ei snat ur al chol est er ol ? 3. Whatwoul di ti mpl yi fami xt ur ehasanenant i omer i cexcess( ee)of40%? 8. 4Nomencl at ur eofEnant i omer s 8. 4. 1DandLConf i gur at i ons 89 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Unt i l1951, t heexper i ment aldet er mi nat i onofabsol ut e( oract ual )conf i gur at i onwasdi f f i cul t . Absol ut econf i gur at i oni st hespat i alar r angementofsubst i t uent satast er eogeni ccent er . Nei t hert hesi gnnort hemagni t udeofr ot at i oncant el l ust heabsol ut econf i gur at i on. Theabsol ut econf i gur at i onsofgl y cer al dehy desandt ar t ar i caci dhadbeenknown.The absol ut econf i gur at i onof( +) gl y cer al dehy dei sdesi gnat edasD si ncet hehy dr oxy l( OH) gr oup i s at t ached t ot he r i ghtoft he chi r alcar bon;t he absol ut e conf i gur at i on of( ) gl y cer al dehy dei sdesi gnat edasLsi ncet he–OHgr oupi sat t achedt ot hel ef toft hechi r al car bon. The conf i gur at i on of a compound det er mi ned exper i ment al l y wi t h r ef er ence t o gl y cer al dehy desoranyknowncompoundi sr ef er r edt oasr el at i v econf i gur at i on.TheDandL act ual l yr ef er st ot heconf i gur at i onoft het woi somer satt hesecondcar bonf r om t hebot t om. DandLhav enot hi ngt odowi t ht hesi gnsofr ot at i on. 8. 4. 2SequenceRul esf orSpeci f i cat i onofConf i gur ai on–TheCahnI ngol dPr el ogR/ SNot at i onal Sy st em Fort hecompound,2chl or obut aneandmanyot hercompounds,t heDLsy st em i sl ess obv i ousbecauseacompar i sonofgr oupswi t ht hosepr esenti nD( +) gl y cer al dehy decannot bemade.I ti st her ef or edi f f i cul tt oi ndi cat ewhi chenant i omerof2chl or obut anei ti swi t hout usi ngmodel . Ani ndependentsy st em wasdev el opedbyCahn,I ngol dandPr el ogt onameconf i gur at i on wi t houtr ef er encet ogl y cer al dehy des.Sot heDLsy st em hasbeenr epl acedbyt heCahnI ngol dPr el ogsy st em, i nwhi cht hef ourdi f f er entgr oupsonanasy mmet r i ccar bonar er anked accor di ngt oasetofsequencer ul es.Theconf i gur at i oni sspeci f i edbyr el at i v eposi t i onsof al l gr oupswi t hr espectt oeachot heratt hechi r al cent er . SequenceRul es I dent i f yt hesubst i t uent satt hest er eogeni ccent erandr ankt hem i nor derofdecr easi ng pr ecedence. Hi gherat omi cnumberi sgi v enhi gherpr i or i t y .( E. g.I >Br >Se>S>F>O>N>C>H) I ft woormor egr oupscannotbedi scr i mi nat edbyt heat omi cnumber , t hosegr oups ar er ankedaccor di ngt omassnumber , wi t ht hehi ghestmasnumbert aki ngt he 90 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 13 hi ghestpr i or i t y .( E. g.D>H; C>12C) Wher et heat omi cnumber soft woormor eat t achedgr oupsar et hesame, t he at omi cnumberoft henextat om det er mi nest hepr i or i t y .Oner epeat st hepr ocess unt i l t hedi scr i mi nat i onbet weengr oupscanbemade. Doubl eandt r i pl ebondsar ecount edasi ft heywer espl i ti nt ot woort hr eebonds, r espect i v el y . Ci sr ankshi ghert hant r ans. Lonepai rel ect r onsar er egul at edasanat om wi t hat omi cnumber0. Li kepai r s[ ( R, R)or( S, S) ]>Unl i kepai r s[ ( R, S)or( S, R) ] Pr oxi mal gr oups>Di st al gr oups Af t ert hef ourgr oupsat t achedt ot hechi r alcent erhav eal lbeenassi gnedpr i or i t i es,t he mol ecul ei sor i ent edsot hatt hel owestpr i or i t ypoi nt sawayf r om t hev i ewer . Nowt her emai ni ngt hr eehi ghestpr i or i t i es( e. g.a, b, cabov e)ar ecount edi ndecr easi ngor der ( i . e. 12 3) .I ft hi sappear si nacl ockcwi sesense,t heabsol ut econf i gur at i oni sR( r i ghtf r om Lat i nwor d,“ r ect us” ) .I ft hi scount i ngappear si nacount er cl ockwi sesense,t heabsol ut e conf i gur at i oni sS( Lat i nsi ni st er , “ l ef t ” ) . NB.I ft hel owestr anki nggr oupi sei t heratt het oporbot t om ( becauset hesear e t het woposi t i onspoi nt i ngawayf r om t hev i ewer ) ,t her e’ snoneedt or eor i entt he mol ecul e.Wej ustassi gnpr i or i t i est ot her emai ni nggr oupsanddet er mi nei ft he conf i gur at i oni sRorSaccor di ngt osequencer ul e3abov e.I ft hel owestr anki ng gr oupi shor i zont al ,wecani nt er changei twi t ht het oporbot t om gr oup,bear i ngi n mi ndt hati nsodoi ng, onei si nv er t i ngt heconf i gur at i on.Assuch, i fourr eadi ngi sS, t hecor r ectconf i gur at i onshoul dbeR, andv i cev er sa. Sampl ePr obl ems 1. Ar r anget hef ol l owi ngi nor derofi ncr easi ngpr i or i t y : ( a)–CH=CH2, C( CH3) 3,CH2CH2CH2C( CH3) b)–COOCH3, COOH, CH( OCH3)( c)–C( CH3) CH( CH3) CH2Cl 3( 2, 2, 2. Dr awt heenant i omer sof1, 2di chl or obut aneandl abel t hem as( R)and( S) . 3. Det er mi net heabsol ut econf i gur at i onasRorS: 91 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 4. Dr aw t et r ahedr alr epr esent at i onsoft hef ol l owi ngmol ecul es:( a)( R) 2But anol ( b)( S) 3Chl or o1pent ene 5. Dr awFi scherpr oj ect i onsf or :( a)t heSenant i omerof2br omobut ane( b)t heRenant i omerof al ani ne, CH3CH( NH2) COOH( c)t heSenant i omerof3met hy l hexane 7. 5Phy si cal Pr oper t i esofEnant i omer s Enant i omer shav ei dent i cal phy si cal pr oper t i es( densi t y , mel t i ngpoi ntandboi l i ngpoi nt ) , exceptf ort hef i r ect i onoft her ot at i onoft hepl aneofpol ar i zedl i ght . Enant i omer scanhowev ershowdi f f er encesi npr oper t i est hatdependont hear r angementof at omsi nspace.Exampl esar et heenat i omer i cf or msofcar v one. 8. 6Mul t i pl eChi r al Cent er s–Di ast er eomer s Manymol ecul eshav emor et hanonechi r al cent er . 8. 6. 1Speci f i cat i onofConf i gur at i onf orMul t i pl eChi r al Cent er edMol ecul es Consi derf orexampl e, 2, 3di chl or opent anewi t ht wochi r al cent er s: 92 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Theconf i gur at i oni sspeci f i edabouteachoft hechi r alcent er s,usi ngnumber st ot el lwhi ch speci f i cat i onr ef er st owhi chcar bon.Thent heSequenceRul ei sused. PRACTI CE: Dr aw t he st r uct ur e of :( a) ( 4R, 5R) 4, 5di i sopr opy l oct ane ( b) ( 1R, 3R) 1, 3di met hy l cy cl opent ane. 7. 6. 2Chi r al Mol ecul esWi t hTwoSt er eogeni cCent er s Whent her ei smor et hanonechi r alcent eri namol ecul e,t hepot ent i alf orst er eoi somer s i ncr easesaccor di ngl y .Let ’ sconsi dert heami noaci d,t hr eoni ne–i thasf ourst er eoi somer s ( t wopai r sofenant i omer s/ mi r r or i mage, nonsuper i mposabl est er eoi somer s) . I&I I , aswel lasI I IandI Var eenant i omer s.Howev er , I&I I I , I&I V, I I&I I I , aswel lasI I&I Var e notenant i omer sbecauseal lt hesepai r sar enotmi r r or i magedpai r sev ent hought heyar e st er eoi somer s.St er eoi somer st hatar enotr el at edt oeachot herasobj ectandmi r r ori mage ar ecal l eddi ast er eomer s. Di ast er eomer sar ephy si cal l yand chemi cal l ydi f f er entcompounds.Theyhav edi f f er ent r ot at i ons( bot hsi gnandmagni t ude) ,mel t i ngpoi nt s,boi l i ngpoi nt s,sol ubi l i t i es,aswel las bi ol ogi cal pr oper t i es. I ngener al ,t henumberofopt i cal l yact i v ei somer sf oramol ecul ei sgi v enbyt heexpr essi on 2n.#ofenant i omer s=2n+1; wher eni mpl i est henumberofasy mmet r i ccent er s. Pr act i ce:Assi gnR, Sconf i gur at i onst oeachchi r al i t ycent eri nt hef ol l owi ngmol ecul es.Whi char e enant i omer sandwhi char edi ast er eomer s? 8. 6. 3Achi r al Mol ecul esWi t hTwoSt er eogeni cCent er s–MesoCompounds A speci alcasear i seswhenamol ecul ehast wochi r alcent er st hatcar r yt hesamef our gr oups, butwhi char eopposi t ei nconf i gur at i on.Sev er alex ampl escanbeci t ed; t ar t ar i caci d, 2, 3but anedi ol and3, 4di met hy l hex anear esomegoodexampl es. 93 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Consi dert ar t ar i caci df orex ampl e: IandI Iar enoti dent i calandar et her ef or eenant i omer s.Howev er , I I IandI Vbecomei dent i cal o byr ot at i ng180.Thi si sbecauset her ei sapl aneofsy mmet r ybet weenC2andC3bond, maki ngonehal foft hemol ecul eami r r ori mageoft heot herhal f .Hence,t hecompoundi s achi r al .Achi r almol ecul est hathav est er eogeni ccent er sar ecal l edmesocompounds.Meso compounds gi v el ess t han t he 2n numberofopt i cali somer s.The meso f or m i sa di ast er eomerofeachoft heenant i omer i cf or m oft ar t ar i caci dandi ti sopt i cal l yi nact i v e. Onl yt hr eef or msoft ar t ar i caci dex i stal t houghf ourar epr edi ct edbyt he2nex pr essi on–t wo enant i omer sandonemeso.Thepr oper t i esoft het woenant i omer sar et hesame,but di f f er entf r om t hoseoft hemesof or m. Sampl ePr obl ems/ Pr act i ce 1. Doesci s1, 2di met hy l cy cl obut anehav eanychi r al i t ycent er s?I si tchi r al ? 2. Whi choft hef ol l owi ngst r uct ur esr epr esentmesocompounds? 3. Whi choft hef ol l owi nghav eamesof or m?( a)4, 6Di et hy l nonane( b)2, 3Di br omobut ane ( c)2, 3Di br omopent ane( d)2, 4Di br omopent ane 8. 7Fi scherPr oj ect i onandChi r al Cent er s I naFi scherpr oj ect i on, t hemosti mpor t antf unct i onal gr oupi spl acedatt het opandt hemai n chai noft hemol ecul ei sv er t i cal .Consi dergl y cer al dehy desf orexampl e: I ngener al , amol ecul ei nt hr eedi mensi onscanbeconv er t edt oaFi scherpr oj ect i on. I nor dert oconv er toneFi scherpr oj ect i ont oanot heri dent i calst r uct ur e,anyt wopai r sof subst i t uent sl i nkedt ot hechi r alcar bonneedbei nt er changed.Thi si sawayt ot estf or 94 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 i dent i t y . Ont heot herhand, i fonl yonepai rofgr oupi si nt er changed, apr oj ect i onofi t senant i omeri s obt ai ned. AFi scherpr oj ect i onf or mul amayber ot at ed180oi nt hepl aneofapaper , butnot90oor270o t oconv er ti nt oani dent i cal st r uct ur e.A180or ot at i onl eadst oani dent i cal st r uct ur e, whi l e90o r ot at i onr esul t si nanenant i omer i cst r uct ur e. Sampl ePr obl ems/ Pr act i ce 1. Conv er tt hef ol l owi ngt et r ahedr al r epr esent at i onof( R) 2but anol i nt oaFi scherpr oj ect i on: 2. Whi choft hef ol l owi ngFi scherpr oj ect i onsr epr esentt hesameenant i omer ? 95 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 3. Dr aw3Df or mul asf ort hef ol l owi ngst r uct ur es: 4. Ar et hef ol l owi ngpai r sofFi scherpr oj ect i onst hesame, orar et heyenant i omer s? 5.Mar kt hei dent i cal st r uct ur es( i fany )i nt hef ol l owi ng: When a Fi scherpr oj ect i on i s dr awn f ora mul t i pl e chi r al cent er ed mol ecul e,and l i ke 96 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 subst i t uent sar eont hesamesi deoft heFi scherpr oj ect i on,i ti sdescr i bedast heer y t hr o di ast er eomer s.When l i kesubst i t uent sar eon opposi t esi des,t hemol ecul ei sa t hr eo di ast er eomer . Twodi ast er eomer st hathav eadi f f er entconf i gur at i onatonl yonechi r alcent erar ecal l ed epi mer s. 8. 8Racemi cMi xt ur esandThei rResol ut i on Ar acemi cmi xt ur eorr acemat ei sami xt ur eofequal amount s( 50: 50)ofbot henant i omer sof acompound.I ti sdenot edas( +)orbyt hepr ef i xdlt oi ndi cat eami xt ur eodext r or ot ar yand l ev or ot ar yf or ms.I ti sopt i cal l yi nact i v ebecauset he( +)r ot at i onf r om oneenant i omerexact l y cancel st he( )r ot at i onf r om t heot her .Thepr ocessbywhi char acemi cmi xt ur ei sf or med f r om chi r almat er i al si scal l edr acemi zat i on.Racemi cmi xt ur esar eof t enf or medwhen achi r al subst ancesar econv er t edt ochi r al ones. Apai rofenat i omer shasi dent i calpr oper t i es,butt her esul t i ngr acemat eof t enhasdi f f er ent pr oper t i es f r om ei t heroft he pur e enant i omer s.Ther ef or e,separ at i on i s di f f i cul t .The separ at i onofar acemat ei nt oi t senant i omer si scal l edr esol ut i on. 97 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 TOPI C9: ALKYNES 9. 1I nt r oduct i on, St r uct ur eandBondi ng Hy dr ocabonst hatcont ai nadoubl yunsat ur at edf unct i onalgr oup( i . e. ,acaboncar bont r i pl e bond) . Gener al f or mul a: CnH2n-2, f ornoncy cl i cal ky nes. Maybe monosubst i t ut ed ( t er mi nal )ordi subst i t ut ed ( i nt er nal ) .Monosubst i t ut ed/ t er mi nal al ky neshav et hei rt r i pl ebondatt heendofacar bonchai n,RC≡CH.Di subst i t ut ed/ i nt er nal al ky neshav et hei rt r i pl ebondswi t hi nt hecar bonchai n, RC≡CR. Hy br i di zat i oni ssp, whi l egeomet r yi sl i near . 9. 2Nomencl at ur eofAl ky nes TheusualI UPACr ul esf ornami nghy dr ocar bonsar ef ol l owed, butt hesuf f i x–anei sr epl aced wi t h y ne. Pr act i cePr obl ems 9. 3Phy si cal Pr oper t i esandSt abi l i t yofAl ky nes Nonpol ar , butsl i ght l ymor epol art hanal kanesandal kenes I nsol ubl ei nwat er , butsol ubl ei nor gani csol v ent s Lowdensi t y Sl i ght l yhi gherboi l i ngpoi ntt hancor r espondi ngal kanesandal kenes Li keal kenes, t hemor ehi ghl ysubst i t ut edi nt er nal al ky nesar emor est abl e Bycompar i ngt her mody nami cdat aofal ky nesandal kenes,i tcanbeseent hatt he“ ext r a”Π bondi nanal ky nei sweakert hant heal keneΠbond Exampl e: ∆Hf or1hexy ne=290kJ/ mol andf or1hexene=126kJ/ mol Sampl ePr obl em: Compar et hest abi l i t yof1hexy neand3hexy ne. 9. 4Sour cesandPr epar at i onofAl ky nes 98 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Lesscommont hanal kenes, bot hi nt hel abandi nl i v i ngor gani sms I t ’ spr epar edonav er yl ar gescal ef r om cal ci um car bi de,CaC2 whi chi spr epar edf r om l i mest one, CaCO3. I nt hel abor at or y , al ky nesar epr epar edbyal ky l at i onofacet y l eneandbyel i mi nat i onr eact i ons. Al ky l at i on ofAcet y l ene:Acet y l ene,bei ng aci di c,i sconv er t ed t oi t sconj ugat ebaseby t r eat mentwi t hsodami de( sodi um ami de,NaNH2) .Thenanal ky lhal i dei saddedt ot he r esul t i ngsol ut i onofsodi um acet y l i de. Mechani sm Exampl es: PRACTI CEPROBLEMS 1. Out l i ne t he ef f i ci entsy nt heses oft he f ol l owi ng al ky nes f r om acet y l ene and any necessar yor gani cori nor gani cr eagent s: ( a)1Hept y ne( b)2Hept y ne ( c)3Hept y ne 2. Whati st heal ky nepr oductf r om t her eact i onoft hef ol l owi ngwi t hsodi um ami de, NaNH2: 2, 2Di br omopr opane ( b) 1, 1Di br omooct ane ( c) 1, 2Di br omohexane ( d) 2, 3Di br omohexane 3. Whati st hepr oductoft her eact i onofCH3C≡C: wi t heachoft hef ol l owi ng: ( a)2br omopr opane ( b)1i odooct ane ( c)( R) 2br omohexane ( d)et hanol ( e) br omobenzene( f )et hy l t osy l at e El i mi nat i onReact i ons: Doubl edehy dr ohal ogenat i onofger mi nal orv i ci nal di hal i de. NB.Thet er mi nalal ky nepr oducti saci di cenought ot r ansf erpr ot ont oami deani on.Ther ef or e,an addi t i onal1equi v al entofbase( NaNH2)i sr equi r ed.So3equi v al ent sofNaNH2 ar eusedi nt he r eact i on. 99 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Exampl es: PRACTI CEPROBLEM Show,bywr i t i nganappr opr i at eser i esofequat i ons,how y oucoul dpr epar epr opy nef r om eachof t hef ol l owi ngcompoundsasst ar t i ngmat er i al s.Youmayuseanynecessar yor gani cori nor gani c r eagent s: ( a)2Pr opanol( b)1Pr opanol( c)I sopr opy lbr omi de ( d)1, 1Di chl or oet hane ( e) Et hy l al cohol 9. 5React i onsofAl ky nes 8 Four( 4)maj ort y pesofr eact i onsar econsi der ed:r eact i onsshowi ngt heaci di t yoft er mi nal al ky nes, addi t i onr eact i ons, met al ammoni ar educt i onofal ky nesandozonol y si s. 9 Aci di t yofTer mi nalAl ky nes:( Al r eadydi scussedi nSec.1. 4) :RC≡CH +B: RC≡C:+BH 10 Addi t i onReact i ons Hy dr ogenat i on: I ti sanel ect r ophi l i caddi t i onr eact i on. Wi t ht heLi ndl ar ’ scat al y st( Pd/ CaCO3/ qui nol i ne) , t her ei spar t i al r educt i onoft he al ky net oci sal kene.Hence, t her eact i oni sst er eospeci f i c, y i el di ngonl yt hesy n addi t i onpoduct . Addi t i onofHy dr ogenHal i de, HX o Wi t hexcessHX, ger mi nal di hal i desar ef or med. o Or derofReact i v i t yofHX:HI>HBr>HCl>HF o HBr( notHIorHCl )addst oal ky nesbyaf r eer adi cal mechani sm whena per oxi dei spr esenti nt her eact i onmi xt ur e.Ther egi osel ect i v i t yi sAnt i - 100 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 Mar kov ni kov . Hal ogenat i on:2 mol es ofhal ogen ar e consumed and a t et r ahal i de i sf or med. Howev er ,i ft heal ky neandt hehal ogenar epr esenti nequi mol aramount s,adi hal i de wi t hanant ist er eochemi st r yr esul t s. Hy dr at i on: Reagenti saqueousaci dwi t hmer cur ysal tascat al y st .Forr egi osel ect i v i t y , Mar kov ni kov ’ sr ul ei sf ol l owed. Hy dr obor aat i onOxi dat i on: 11 Met al Ammoni aReduct i onofAl ky nes Reduct i onofGr oupImet al( Li , NaorK)i nl i qui dammoni aconv er t st heal ky net ot r ans( orE) al kene. 12 Ozonol y si sofAl ky nes 101 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er Depar t mentofChemi st r y , Sci enceCol l ege, Uni v er si t yofLi ber i a LECTURENOTESFORCHEM 201–ORGANI CCHEMI STRYI–SEM I 2017/ 2018 PROBLEM SETNO.9 1. Wr i t est r uct ur al f or mul asandgi v et heI UPACnamesf oral l al ky nesofmol ecul ar , C5H8. 2. Namet hef ol l owi ngcompounds: 3. Whatpr oduct swoul dy ouex pectf r om t hef ol l owi ngr eact i ons? 4. Gi v et hest r uct ur esoft hr eei somer i cdi br omi dest hatcoul dbeusedasst ar t i ngmat er i al sf or t hepr epar at i onof3, 3di met hy l 1but y ne. 5. Whatpr oductwoul dy ouobt ai nbyhy dr at i onoft hef ol l owi ngal ky nes? 6. Whatal ky neswoul dy oust ar twi t ht opr epar et hef ol l owi ngcar bony l compounds? 7. Usi nganyal ky neneeded, howwoul dy oupr epar et hef ol l owi ngal ky nes?( a)t r ans2Oct ene ( b)ci s3Hept ene( c)3Met hy l 1pent ene 8. Showt het er mi nal al ky neandal ky l hal i def r om whi cht hef ol l owi ngpr oduct scanbeobt ai ned. I ft wor out esl ookf easi bl e, l i stbot h.( a)CH3CH2CH2C≡CCH3 ( b)( CH3) HC≡CCH2CH3 2C 9. Howcoul dy oupr epar eci s2but enest ar t i ngf r om pr opy ne, anal ky l hal i de, andanyot her r eagent sneeded? 10.Pr epar eoct anef r om 1pent y ne. 11.Sy nt hesi zeci s2hexenef r om 1pent y neandanyal ky l hal i deneeded.[ HI NT: Mor et hanone st epi sr equi r ed. ] 12.I l l ust r at eaccept abl emechani smsf oreachoft hef ol l owi ngr eact i ons: 13.Whatal ky newoul dy oust ar twi t ht opr epar eeachoft hef ol l owi ngcompoundsbya hy dr obor at i on/ oxi dat i onr eact i on? 102 Compi l edandpr epar edbyChemi st r yDepar t ment( Or gani cChemi st r y )-Cour seLect ur er