Aldehydes, ketones and carboxylic acids

Aldehydes and ketones

Carbonyl C is electrophilic: nucleophilic addition (HCN, NaHSO₃, alcohols → hemiacetal/acetal, Grignard → alcohol after hydrolysis, ammonia derivatives → imines/hydrazones).

Aldehydes oxidise to acids (Tollens’ silver mirror, Fehling’s/Benedict’s with aliphatic aldehydes). Ketones generally resist mild oxidation — distinction test.

Aldol condensation: enolate + carbonyl → β-hydroxy carbonyl; dehydration gives α,β-unsaturated product. Crossed aldol needs planning to avoid mixtures.

Carboxylic acids

Acidity: electron-withdrawing groups increase acid strength (Cl₃CCO₂H > Cl₂CHCO₂H > ClCH₂CO₂H > CH₃CO₂H). Aromatic acids: benzoic acid; ortho substituents can increase acidity via intramolecular H-bonding to carboxylate in some cases.

Reactions: formation of acid chlorides, anhydrides, esters (Fischer esterification), amides. Decarboxylation of β-keto acids and malonic esters synthesis appear as named patterns in NCERT.

Preparation and tests

Ozonolysis of alkenes gives carbonyl fragments. Oxidation of 1° alcohols and aldehydes; 2° alcohols to ketones. Nitriles hydrolyse to acids.

2,4-DNP test (yellow/orange precipitate), iodoform test for methyl ketones and ethanol, Tollens and Fehling for aldehydes — tie to your qualitative practical list.