ALDEHYDES AND ALDEHYDES AND KETONESKETONES

Aldehydes and Ketones

CH

RO C

R

RO

Aldehyde Ketone

CH

HO

lone Pairs

bond - two overlapping 2p orbitals

bond

bond- overlapping 1s H-orbital and sp2 C-orbital

C O

H3C

H118o

121o

C C

H

H

H

H118o

121o

C O

H3C

HC O

H3C

H

Resonance Structures

Most Reactive Group –

electrons + polarisation

Names al – aldehydes, one - ketones

C O

H

HC O

H3C

H

C O

CH3CH2

H

C O

CH3CH2CH2CH2

H

Methanal(formaldehyde)

Ethanal(acetaldehyde)

Propanal Pentanal

Nomenclature of Aldehydes

If the aldehyde group is attached to a ring,

Nomenclature of Ketones

Oxidation

An aldehyde has a greater partial positive charge on its carbonyl carbon than does a ketone

• The carbonyl carbon of an aldehyde is more accessible to the nucleophile

• Ketones have greater steric crowding in their transition states, so they have less stable transition states

• Steric factors contribute to the reactivity of an aldehyde

1. Redox reactions

RCH

O

KMnO4

or CrO3R C

OH

O

H2R

R'

C O

R

R'

CH

OH

Reactions

RCH

O

H2red.

RCH2OH

2. Addition: AN

H

R

C O + H2O

H

R

COH

OH

Addition of water

Aldehyde hydrate

(ketone: )

R

R'

C O + NaHSO3

R

R'

CSO3

-Na+

OH

Addition of bisulfite

Bisulfite

Addition of NH3

Aldehyde ammonia

(ketone: )

Addition of HCN

Cyanohydrine

H

R

C O + NH3

H

R

CNH2

OH

R

R'

C O + HCN

R

R'

CC

OH

N

3. Condensation reactions (addition followed by elimination)

Ammonia derivatives

Primary amine

Schiff base

O + C

R'

R H

H

N Y

R

R'

C Y N

N R"C

R'

RH

H

N R"R

R'

C O +

Hydroxylamine

Hydrazine

Hydrazone

O + C

R'

R H

H

N OHR

R'C OH N

O + C

R'

R H

H

N NR

R'

C NH2 N H

H

Oxime

Phenylhydrazine

2,4-dinitrophenylhydrazine

2,4-dinitrophenylhydrazone

Phenylhydrazone

O + CR'

R HH

H

N N

O + CR'

R H

H

N N

H

NO2

NO2

Aldol condensation

Aldol

OH-CH2 CH CH C H

R OOH R'

CH2 C H + CH2 C H

R O R' O

Reaction with alcohol

Acetal (condensation!)

Hemiacetal (addition!)

R C H + HO

O

R' R C O R'

H

OH

O R

H H

O

O

R'

R'R C H + HO R' R C

Keto–Enol Tautomerism

Oxidation of a Primary Alcohol

Reduction by Addition of a Hydride Ion and a Proton

Aldehydes and ketones react with nucleophiles to formaddition products: nucleophile addition reactions

Water adds to an aldehyde or ketone to form a hydrate

Hydration of Aldehydes and Ketones

HOHHOH

CC••••OO ••••

HOHO CC OO HH••••

••••

••••

••••

RR

R'R'

RR

R'R'

Alcohols Under Analogous Reaction

with Aldehydes and Ketones

R"OR"OHH

CC••••OO ••••

RR

R'R'

R"OR"O CC OO HH••••

••••

••••

••••

RR

R'R'

Product is called Product is called a a hemiacetalhemiacetal..

HClHCl

2CH2CH33CHCH22OOHH++

+ H+ H22OO

Benzaldehyde diethyl acetal (66%)Benzaldehyde diethyl acetal (66%)

Example

CHCH

OO CH(CH(OOCHCH22CHCH33))22

Reaction with Reaction with Primary Amines:Primary Amines:

IminesImines

If the nucleophile that adds to the aldehyde or ketone isan O or an N, a nucleophilic addition–elimination reactionwill occur

HH22NN

RR

CC OO••••

++•••• •••• HH

a carbinolaminea carbinolamine

CC OOHHNN

RR

••••

••••

••••

NN

RR

CC + + HH22OO(imine)(imine)••••

Imine (Schiff's Base) Formation

CHCH33NNHH22CHCH

OO

++

CH=CH=NNCHCH33 + + HH22OO

N-N-Benzylidenemethylamine (70%)Benzylidenemethylamine (70%)

Example

Reaction with Derivatives of Ammonia

HH22NN GG ++ RR22CC OO RR22CC NNGG ++ HH22OO

HH22NN OHOH RR22CC NNOHOH

hydroxylaminehydroxylamine oximeoxime

Reaction with Derivatives of Ammonia

HH22NN GG ++ RR22CC OO RR22CC NNGG ++ HH22OO

HH22NN OHOH RR22CC NNOHOH

hydroxylaminehydroxylamine oximeoxime

HH22NN NHNH22 RR22CC NNNHNH22

hydrazinehydrazine hydrazonehydrazone

etc.etc.

+ H+ H22NNNHNH22

+ H+ H22OO

(73%)(73%)

Example OOCC NNNHNH22

CC

CCHCCH33

Example OO

+ H+ H22NNNHNH

phenylhydrazinephenylhydrazine

+ H+ H22OO

CCHCCH33

NNNHNH

a phenylhydrazone (87-91%)a phenylhydrazone (87-91%)

An aldol addition product loses water to form an aldol condensation product

2RCH2RCH22CHCH

OONaOHNaOH

RCHRCH22CHCH

OHOH

CHCHCHCH

OO

RR

Aldol Condensation

Aldol Addition of Acetaldehyde

AcetaldolAcetaldol(50%)(50%)

NaOH, HNaOH, H22OO

5°C5°C2CH2CH33CHCH

OO

CHCH33CHCH

OHOH

CHCH22CHCH

OO

Product is called Product is called a a hemiacetalhemiacetal..

ROROH, HH, H++

Hemiacetal reacts further in acid to yield an acetal

R"OR"O CC OO HH••••

••••

••••

••••

RR

R'R'

R"OR"O CC OROR••••

••••

••••

••••

RR

R'R'

Product is called Product is called an an acetalacetal..

Formaldehyde

formaldehyde cannot form an enolateformaldehyde cannot form an enolate

formaldehyde is extremely reactiveformaldehyde is extremely reactive toward nucleophilic additiontoward nucleophilic addition

OO

HCHHCH

Acrolein

HH22CC CHCHCHCH

OO

HH22CC CHCHCHCH

OO

Acrolein

Acrolein

HH22CC CHCHCHCH

OO