Aldehydes and ketones (A-level only)

Aldehydes are readily oxidised to carboxylic acids.

Chemical tests to distinguish between aldehydes and ketones including Fehling’s solution and Tollens’ reagent.

Aldehydes can be reduced to primary alcohols, and ketones to secondary alcohols, using NaBH₄ in aqueous solution. These reduction reactions are examples of nucleophilic addition.

The nucleophilic addition reactions of carbonyl compounds with KCN, followed by dilute acid, to produce hydroxynitriles.

Aldehydes and unsymmetrical ketones form mixtures of enantiomers when they react with KCN followed by dilute acid.

The hazards of using KCN.

Students should be able to:

• write overall equations for reduction reactions using [H] as the reductant

• outline the nucleophilic addition mechanism for reduction reactions with NaBH₄ (the nucleophile should be shown as H⁻)

• write overall equations for the formation of hydroxynitriles using HCN

• outline the nucleophilic addition mechanism for the reaction with KCN followed by dilute acid

• explain why nucleophilic addition reactions of KCN, followed by dilute acid, can produce a mixture of enantiomers.