ALKE NES
(Olefins) general molecular formula: CnH2n
Nomenclature
The -ane suffix of alkane is replaced by –ene
IUPAC Nomenclature
2
1
4
3
5
5
4
2
3
3
1
2
4-M ethyl-1-pentene
2-Pentene
1
4
5
6
8
7
2,5-Dimethyl-2-octene
5
2 3
4
1
2-Ethyl-1-pentene
CH3
1 2
3 4
5 6
CH3CH CHCH2C CH3
CH3
5,5-Dimethyl-2-hexene
CH3
2 1
4 3
CH3CH CHCH2Cl
CH3
CH3C CHCH2CH CH3
6
3 4 5
1 2
2,5-Dimethyl-2-hexene
1-Chloro-2-butene
OH has higher priority then double bond:
OH
1
4
5
2
3
OH
1
3-Penten-1-ol
6
2
5
3
4
Cyclohex-3-en-1-ol
In Cycloalkenes
3
1
2
4
1
5
6
3-M ethylcyclohexene
2
3
5
3
4
1-M ethylcyclopentene
Cl
1
6
2
5
4
3,5-Dimethylcyclohexene
5
1
Cl
4
3
2
4,4-Dichlorocyclopentene
If there is more than one double bond in a compound
1
2
3 4
5
CH2 CH CH2CH CH2
1
2
4
3
CH2 CH CH CH2
1,4-Pentadiene
1,3-Butadiene
4
2
5
3
6
2
1
4
3
5
6
7
1
1-Ethyl-1,4-cyclohexadiene
6-M ethyl-2,4-heptadiene
*Common names (Historical)
CH2
CH
Vinyl Group
CH2
CH Cl
Vinyl Chloride
CH2
CH CH2
Allyl Group
CH2
CH CH2 OH
Allyl Alcohol
CH2 CH2
Common: Ethylene
IUPAC: (Ethene)
CH3CH CH2
Propylene
(Propene)
3 2CH3 1
CH3C CH2
Isobutylene
(2-M ethylpropene)
Cis-Trans Isomerism
2-Butene can exist in two isomeric forms:
These are configurational isomers
CH3
CH3
CH3
C C
H
C C
H
H
Cis-2-butene
Cl
H
1 2
C C
CH3
Trans-2-butene
Cl
Cl
H
H
1 2
C C
H
H
Cis-1,2-dichloroethene
H
3
1
Cl
Trans-1,2-dichloroethene
2
1
4
H
6
5
3
Trans-3-hexene
4
5
2
Cis-3-hexene
6
The Z–E system (Geometrical isomers)
We examine the two groups attached to one carbon atom of the double bond and
decide which has higher priority then we repeat that operation at the other carbon.
* If the higher-priority groups are on the same side, use the prefix
Z-(Zusammen; together).
* If the higher-priority groups are on opposite sides use
E-(Entgegen; opposite). Cl
Cl
H
F
1 2
C C
CHCl= CHF
H
1 2
C C
H
H
(Z)-1-Chloro-2-fluoroethene
H
F
(E)-1-Chloro-2-fluoroethene
F
H
Cl
Br
2 1
C C
Br
Cl
2 1
C C
(Z)-2-Bromo-1-chloro-1-fluoroethene
F
(E)-2-Bromo-1-chloro-1-fluoroethene
I > Br > Cl > S > F > O > N > C > H
Priority
4
2
1
5
4
1
5
3
2
Br
(Z)-3-Bromo-2-pentene
3
Br
(E)-3-Bromo-2-pentene
Preparation of Alkenes
(1)
(2)
(3)
0
CH3CH2 OH + Conc. H2SO 4
CH3CH2CH2Br + KOH/ EtOH
Propyl bromide
CH3CH2CHBr2 + Zn
Propyldiene bromide
160-170 C
CH2 CH2
CH3CH CH2 + KBr + H2O
MeOH
ZnBr2 + CH3CH CH2
Propylene
MeOH
ZnBr2 + CH3CH CH2
Propylene
Br
CH3CHCH2Br + Zn
Propylene bromide
(4) Wurtz synthesis:
CHEMICAL REACTIONS OF ALKENES
I – Hydrogenation (Reduction) of Alkenes (Addition of H2)
CH2 CH2
H2/ Pt
CH3 CH3 (Catalytic Hydrogenation)
H2/ Pt
Cyclohexene
Cyclohexane
CH3
H2/ Pt
CH3
Cis-1,2-Dimethylcyclohexane
CH3
H
CH3
H
1,2-Dimethylcyclohexane
II – Electrophilic Addition of Alkenes
(A) Addition of hydrogen halides (hydrohalogenation) HX
CH2
CH2
+
HBr
Ether
CH3 CH2Br Ethyl Bromide
Cl
+ HCl
Chlorocyclopentane
Ether
Mechanism (Ionic Reaction)
CH2
CH2 +
Ethene
H X
Hydrogen Halide
HBr
+
CH2 CH3
Carbocation
X
-
XCH2 CH3
Ethyl Halide
BrCH2CH3
Ethyl Bromide
For Unsymmetrical alkane (Markovnikov's Rule)
CH3
CH3
CH3
C CH2
HBr
Ether
CH3 C Br
CH3
CH3
2-M ethyl-1-propene
CH CH2Br
Not
CH3
2-Bromo-2-methylpropane
I
Not I
HI
1-Butene
2-Iodobutane
HBr
Br
CH3
CH3
Markovnikov's Rule
In the addition of HX to an alkene, the H+ adds to the carbon atom of the double
bond that already has the greater number of hydrogen atoms.
Br
CH2 CH CH3
+ HBr
CH2
CH CH3
Mechanism (Ionic reaction)
H
CH2 CH CH3 +
H X
+
X
CH2 CH CH3
M ore stable carbocation
H
CH2 CH CH3
+
H X
+
X
CH2 CH CH3
Less stable carbocation
{Not by this way}
X
-
CH3 CH CH3
-
X
CH2 CH2 CH3
Not formed
Radical Addition to Alkenes
Addition of hydrogen halide in presence of peroxide this reaction is
under free radical condition (Anti Markovnikov's Rule).
R O O R
Peroxide
RO
+ H Br
2 RO
R OH + Br
Br
CH3 CH CH2
Br
CH3 CH2 CH2
CH3 CH2 CH3
0
1 Radical (less stable)
H Br
Peroxide
Anti Markovnikov's
CH3 CH CH2Br
CH3 CH2 CH2Br
0
2 Radical (M ore stable) M ajor products
(B) Addition of water to Alkenes: (Hydration)
Acid-catalyzed hydration
The reaction follows Markovnikov's rule
CH3
CH3
C CH2
+ H2SO4/ H2O
CH3 C CH3
OH
tert-Butyl Alcohol
CH3
2-M ethyl-1-propene
OH
CH3CH2CH CH2
1-Butene
H2O/ H+
CH3CH2CH CH3
2-Butanol
H2SO4/ H2O
CH3
OH
CH3
OH
H2SO4/ H2O
Mechanism
CH3 CH2 CH CH2
+
+
H+
CH3 CH2 CH CH3
0
2 Carbocation
(M ore stable)
Not CH3CH2CH2CH2
0
1 Carbocation
(Less stable)
+
OH2
+
CH3 CH2 CH CH3
2-Butyl carbocation
H
+
O
H2O
H
CH3 CH2 CH CH3
Oxonium ion
CH3 CH2 CH CH3
Oxonium ion
OH
H2O
This reaction is acid-catalyzed
+
CH3 CH2 CH CH3 + H3O
2-Butanol
the acid is not consumed
(C) Addition of Halogens
Cl2/CCl4 or Br2/CCl4
Br
CH3CH CHCH3
+
Br2
CCl4/ R.T.
Br
CH3CH CHCH3
Br
+
Br2
CCl4
Br
(D) Addition of Mercuric acetate (Oxymercuration- Demercuation)
CH3
CH3CH2 C CH2
CH3
(1) Hg(OA) 2 / THF/ H 2O
(2) NaBH 4
CH3CH2 C OH
CH3
2-Hydroxy-2-methylbutane
(tert-pentanol)
2-M ethyl-1-butene
OAC
Mechanism
+
Hg
CH3CH2 C CH2
CH3
OAC
Oxymercuration
OAC
Hg
CH3CH2 C
CH2
CH3
H2O
CH2 HgOAC
CH2 HgOAC
-HOAC
CH3CH2 C OH
CH3CH2 C OH2
+
CH3
CH3
An organomercury intermediate
CH3
NaBH4
Demercuration
CH3CH2 C OH
CH3
-
OAC
(E) Hydroboration of Alkenes (Anti- Markovnikov addition)
CH3CH CH2 + H BH2
Propene
CH3CH CH2
(CH3CH2CH2)2BH
CH3 CH CH2 BH2
H
CH3CH CH2
3 CH3CH2CH2 OH
Propyl alcohol
Hydroboration
(CH3CH2CH2)3B
Tripropylborane
H2O 2/ OH
Oxydation
Mechanism
H3C
H
H3C
C C
H
H
H
H
B
H Act as electrophile

H

C
C
H
H
B H
H
H3C
H
C

H
Cyclic four-center
Transition state
C
H
H
H
BH2
Alkylborane
The other B-H bonds
of alkylborane can undergo
similar additions;leading finally
to a trialkylborane
(1) Hg(OAC)2/ THF/ H2O
(2) NaBH4
CH3
CH3 C CH CH2
CH3 OH
CH3 C CH CH3
CH3
CH3
(1) (BH3)2/ THF
(2) H2O2/ NaOH
CH3
H2SO4/ H2O
CH3 C CH2 CH2OH
CH3
CH3 OH
CH3 C CH CH3
CH3
III- Oxidation of alkenes
(KMnO4) or (OsO4)
 This
reaction is Syn-additiom of two hydroxyl groups; the attack
of the 2C atoms of C=C takes place from the same side.
OH OH
CH3CH CH2
Propane
+
KMnO4
Cold
H2O
+ MnO2
CH3CH CH2
Brown ppt
1,2-Propanediol
(Propylene glycol)
OH
+
KMnO4
Cold
+ MnO2
H2O
OH
Mechanism for Syn-addition of alkenes
(Syn Hydroxylation)
C
O
H2O
O
Mn
O
O
C C
O
O
Mn
-
O
O
C
C
+ MnO 2
OH OH
-
O
C
Os
O
C
O
O
C
O
H2O
O
Os
O
O
C
C
OH OH
+ Os
* Ozonolysis of alkenes (Addition of ozone O3)
CH3
CH3
H
0
C C
CH3
O3 / - 78 C
Zn/ H2O / HOAC
O H
CH3
0
1)O3/ - 78 C
2)Zn/ H2O/ HOAC
CH3
CH3
CH3
H
H
Formaldehyde
CH3
2
C O
CH3
1)O3 / - 78 C
H
C O
2)Zn/ H2O / HOAC
CH3
C O + O C
CH3
0
C C
H
CH3
Acetone
O
Ozonide
C C
CH3
CH3
C C
CH3 O
H
CH3
H
CH3
Acetone
+
O C
CH3
Acetaldehyde
ALKYNE
(Acetylenes)
M.F. = CnH2n-2
1
2 3
5
4
3 2 1
CH3 C C CH2 Cl
7
1
4
3-M ethyl-1-pentyne
1-Chloro-2-butyne
CH3
5
3
6
4
1-Heptyne
2
CH3
CH3 CH CH2CH2C CH
5
6
4
3 2 1
CH3 C CH2 C CH
3
5 4
2 1
CH3
4,4-Dimethyl-1-pentyne
5-M ethyl-1-hexyne
HC CH
Ethyne (acetylene)
Ethynylcyclohexane
( HC C : ethynyl gp)
1
2
3
5
6
7
CH3C CH
Propyne (methylacetylene)
CH3C CCH3
2-Butyne (dimethylacetylene)
4
1,5-Heptadiyne
* Radicals: Alkynyl
H C C
Ethynyl
CH3CH2 C C
1-Butynyl
PREPARATION OF ALKYNES
1- By the action of ethanolic KOH on ethylene bromide (vicinal dihalide)
The reaction proceeds in two steps.
CH2Br CH2Br + KOH/ Ethanol
Ethylene bromide
CH2 CHBr + KBr + H2O
(Vicinal dihalide)
CH2 CHBr + KOH/ Ethanol
Vinyl bromide
CH CH
+ KBr + H2O
2- By the action of KOH/EtOH on ethylidene chloride (Geminal dihalide)
CH2CHCl2 + KOH/ EtOH
Ethylidene chloride
CH2 CHCl
KOH
CH CH
(Geminal dihalide)
3- Using sodamide in liquid ammonia
Br
Br
CH CH
+ 2 NaNH2
CH CH
+ 2 NaBr + 2 NH3