CHAPTER 11

ALDEHYDE AND KETONE

Structure of aldehyde and ketone• Aldehyde and ketone = carbonyl compounds

• General formula CnH2nO

C

R

O

H

C

R

O

R

aldehyde ketone

IUPAC Nomenclature for aldehydes and ketones

Compounds Structural formula IUPAC Nomenclature Commom Nomenclature

aldehydes HCOH methanal Formaldehyde

CH3COH ethanal Asetaldehyde

CH3CH2COH propanal Propionaldehyde

CH3CH2CH2COH butanal Butyraldehyde

CH3CH2CH2CH2COH pentanal valeraldehyde

ketones CH3COCH3 propanone Acetone

CH3COCH2CH3 2-butanone Methyethylketone

CH3COCH2CH2CH2CH3 2-pentanone n-propylmethylketone

CH3CH2COCH2CH3 3-pentanone Diethylketone

CH3CH(CH3)COCH3 3-methyl-2-butanone methylisopropylketone

Preparation of aldehydes and ketones

a) Hydration of alkynes

B) Ozonolysis of Alkenes

C) Friedel Crafts Reaction

D) Oxidation of alcohols

Tollens’ “Silver Mirror” Test

ADDITION REACTION OF ALDEHYDES AND KETONES

1) Cyanohydrin Formation

- HCN is added to aldehyde/ketone to form cyanohydrin or hydroxyl nitriles compound

- CN group is easily hydrolyzed to a carboxylic acid in the presence of H2O/H+

2) Catalytic Hydrogenation: Reduction to ROH

3)Reduction to ROH - NaBH4 or LiAlH4 are often used as a reducing agent and followed by

water/dilute acid to convert aldehyde/ketone to alcohols.

4)Grignard Addition- Preparation of ROH

5)Acetal Formation -ROH is added to form hemiacetals then condence with a

second molecule of ROH to produce acetals

6)Addition of amines

REACTION INVOLVING ALPHA HYDROGENS

C

O

CCC

C

• C=O is a strong electronwithdrawing group

• C=O can polarize the adjacent C-H bonds – making -hydrogen weakly acidic

C

O

C

H

C

O

C+ OH- + H2O

-

C

O

C-

C

O-

C

Enolate ion

C

O-

C CC

OH

CC

O

H

H+

Enol formKeto form

Tautomer = interconvertible structural isomers

Aldol Condensation• Aldehyde or ketone molc is added to the C=O of another

by base initiated nucleophilic addition

CROSS ALDOL CONDENSATION- Between 2 different carbonyl compounds. - 1 of the molecule has no -hydrogen