13.7
Aldehydes and Ketones
Structures.
 Two series of organic
compounds containing C=O
carbonyl group.
 Aldehydes have a hydrogen
attached to the carbonyl
group.
 Two groups react
differently and can be
distinguished.
aldehyde
ketone
Aldehydes
Now try these:-
 Named using suffix -
al.
 E.g. HCHO methanal
 CH3CHO ethanal
propanal
pentanal
Ketones
 Name use suffix -one.
 E.g. CH3COCH3




propanone
Ketones with 5 or more
carbons have structural
isomers eg.
CH3COCH2CH2CH2CH3
&
CH3CH2COCH2CH2CH3
Draw the structures and
name these isomers.
 Now try these:
 CH3CH2CH2CH2COCH2CH2CH3
 CH3CH2CH2COCH2CH2CH3
 CH3CH2COCH2CH2CH2CH2CH3
 CH3COCH2CH3
 CH3CH2COCH2CH2CH2CH3
Preparation of aldehydes and
ketones
 Oxidation of alcohols
 Acidified potassium dichromate - heat
under reflux.
 Orange dichromate Cr2O72- is reduced to
green Cr3+ in solution.
 Primary alcohol  aldehyde  carboxylic
acid
 Secondary alcohol  ketone.
Redox reactions
 Oxidation of alcohols are redox reactions.
 Oxidation of ethanol;
 CH3-CH2-OH CH3-CHO + 2H+ + 2e CH3-CHO + H2O CH3COOH + 2H+ + 2e reduction;
 Cr2O72-(aq) + 14H+(aq) + 6e- 2Cr3+ (aq) +7H2O
 orange

green
Reactions - oxidation
 Aldehydes have a hydrogen atom next to
the carbonyl group - easily oxidised.
 Fehlings solution - Cu2+(aq) ions (in alkali)
reduced to Cu+ - blue to brick red.
 Aldehyde oxidised to carboxylic acid.
 Ketones not oxidised easily by either
Fehlings solution or acidified dichromate.
Reactions - reduction
 Powerful reducing agent needed.
 NaBH4 - sodium tetrahydridoborate (III)
 Aldehydes reduced to primary alcohols.
 Ketones reduced to secondary alcohols.
Reactions - addition
 Carbonyl groups can undergo addition
reactions.
 HCN in presence of alkali.
 Adds across C=O to form 2 hydroxynitriles
(cyanohydrins)
 Nucleophilic addition
