H2 Chemistry 16 - Hydroxyl Compounds

> energy required to overcome stronger H bonds bw ROH molecules than weaker id-id attractions bw alkane molecules

no. of e- per molecule to be polarised increases as > energy required to overcome stronger id-id attractions bw molecules

branching causes molecule to become > spherical >

molecule has smaller SA of contact bw adjacent molecules >

< energy required to overcome < extensive id-id attractions bw molecules

reaction: electrophilic addition

r&c: steam, H₃PO₄ catalyst, high temp and pressure

reaction: nucleophilic substitution

r&c: NaOH(aq), heat

aldehyde -> 1^o ROH

reaction: reduction

r&c: LiAlH₄, dry ether/ NaBH₄, methanol

OR H₂(g), Ni catalyst, heat

ketone -> 2^o ROH

reaction: reduction

r&c: LiAlH₄, dry ether/ NaBH₄, methanol

OR H₂(g), Ni catalyst, heat

RCOOH -> 1^o ROH

reaction: reduction

r&c: LiAlH4, dry ether

ROH -> C=C + H₂O

reaction: elimination

r&c: excess conc H₂SO₄, heat

OR Al₂O₃, high temp

1. w/ PCl₅

ROH + PCl₅ -> RCl + POCl₃ + HCl(g)

r&c: dry PCl₅(s), rtp

2. w/ PX3

ROH + PX3 -> 3RX + H3PO3

r&c: dry PX₃, heat

3. w/ SOCl2

ROH + SOCl₂ -> RCl + SO₂(g) + HCl(g)

r&c: dry SOCl2(l), heat

4. w/ HX

ROH + HX -> RX + H₂O

r&c: dry HX(g), heat

OR NaX(s), conc H₂SO₄, heat

aldehyde

1^o ROH + [O] -> RCHO + H₂O

r&c: K₂Cr₂O₇(aq), H₂SO₄(aq), HWID

obs: orange K₂Cr₂O₇(aq) turns green(Cr³⁺)

carboxylic acid

1^o ROH + [O] -> RCOOH + H₂O

r&c: KMnO₄/K₂Cr₂O₇(aq), H₂SO₄(aq), HUR

obs: orange K₂Cr₂O₇(aq) turns green(Cr³⁺)

OR purple KMnO₄(aq) decolourises

ketone

1^o ROH + [O] -> RCOR' + H₂O

r&c: KMnO₄/K₂Cr₂O₇(aq), H₂SO₄(aq), heat

obs: orange K₂Cr₂O₇(aq) turns green(Cr³⁺)

OR purple KMnO₄(aq) decolourises

nothing because they dont undergo oxidation. LOL!

CH3CH(OH)- + 6OH^- + 4I₂ -> RCOO^- + 5I^- + 5H₂O + CHI₃

reaction: positive triiodomethane/iodoform test

r&c: I₂(aq), NaOH(aq), heat

obs: pale yellow CHI₃ seen

ROH + Na -> RO^-Na⁺ + H₂(g)

reaction: redox reaction

obs: effervescence, gas extinguishes lighted splint w/ pop sounds

NS w/ PCl5

test: add PCl5(s) to sample in a dry test tube.

obs: white fumes of HCl(g) evolved for 1^o, 2^o & 3^o ROH

[O]

test: add KMnO₄/K₂Cr₂O₇(aq), H₂SO₄(aq) to sample in test-tube, heat using hot water bath

obs: 1^o, 2^o ROH; orange K₂Cr₂O₇(aq) turns green/KMnO₄(aq) turns colourless

3^o ROH; remains orange/purple

using neutral FeCl₃

test: add neutral FeCl₃(aq) to sample in test tube

obs: violet colouration observed

ES of Br

test: add Br₂(aq) to sample in test tube

obs: orange Br₂(aq) decolourises initially, white ppt of 2,4,6-tribromophenol formed upon adding excess Br₂

> energy required to overcome stronger H bonding bw phenol molecules than weaker id-id attractions bw alkane molecules

bulky non-polar benzene ring hinders formation of effective H bonds bw phenol & H₂O molecule

p-p orbital overlap bw C and O results in delocalisation of lp of e- on O into benzene ring >

formation of partial db character, strengthening C-O bond, > difficult to break>

C-O bond in phenol stronger than ROH

p-p orbital overlap bw C and O results in delocalisation of lp of e- on O of -OH group into benzene ring, benzene ring > e^--rich and susceptible to electrophilic substitution

phenol + RCOCl -> benzoate ester + HCl

reaction: nucleophilic acyl substitution

r&c: Phenol in NaOH(aq), followed by RCOCl, rtp

NaOH(aq) to form phenoxide ion, stronger Nu than phenol

phenol weaker Nu than ROH as p-p orbital overlap results in delocalisation of lp of e- on O into benzene ring >

lp on O less available to attack e^--deficient partially +ve C in RCOOH >

-OH is poor leaving group

strength of acids depends on stability of anion formed >

> stable anion, POE lies more to right, favours formation of anion >

> H+ formed, acid is stronger

stability of anion depends on EDG that intensifies -ve charge, destabilising anion & EWG that disperses -ve charge, stabilising anion

reaction: condensation/ nucleophilic acyl substitution

ROH + R'COOH (REVERSIBLE ARROW) R'COOR + H₂O

r&c: RCOOH, conc H2SO4, heat

OR

ROH + R'COCl -> R'COOR + HCl

r&c: RCOCl, rtp