Aldehydes and ketones (A-level only) revision notes

Aldehydes and Ketones

Naming and Representing Aldehydes and Ketones

• Aldehydes: Named with the suffix -al. The carbonyl group is always at the end of the carbon chain. For example, butanal has a four-carbon chain with a carbonyl group at the first carbon.
• Ketones: Named with the suffix -one. The carbonyl group is located within the carbon chain. For example, butan-2-one has a carbonyl group on the second carbon of a four-carbon chain.

Distinguishing Aldehydes from Ketones

• Tollens' Reagent: A solution of silver nitrate in ammonia that oxidizes aldehydes to carboxylic acids, producing a silver mirror. Ketones do not react.
• Fehling's Solution: A blue solution that contains copper(II) ions. Aldehydes reduce it to a red precipitate of copper(I) oxide, while ketones do not react.

Oxidation of Aldehydes

• Aldehydes can be oxidized to carboxylic acids using oxidizing agents such as potassium dichromate or Tollens' reagent. This reaction involves the addition of oxygen or the removal of hydrogen.

Nucleophilic Addition Reactions

• Carbonyl compounds undergo nucleophilic addition due to the polar C=O bond. Nucleophiles attack the carbon atom, leading to the formation of a tetrahedral intermediate. Common nucleophiles include hydride ions (from NaBH4) and cyanide ions (from KCN).