Chapter 8 — Aldehydes, Ketones and Carboxylic Acids

Chapter 8 of the Class 12 Chemistry NCERT textbook, "Aldehydes, Ketones and Carboxylic Acids", covers these polar carbonyl-group compounds central to organic synthesis, biochemistry, and industrial applications such as solvents, perfumes, plastics, and food preservatives.

• The carbonyl group as the common thread — The chapter is organised around the C=O group, distinguishing aldehydes, ketones and the –COOH of carboxylic acids by what the carbonyl carbon is bonded to, and surveying how each class is prepared from alcohols, alkynes, nitriles and other precursors.
• Reactions and how the compounds are told apart — It develops the characteristic chemistry — nucleophilic addition, aldol and Cannizzaro reactions, reductions and esterification — and uses tests like Tollens' and Fehling's to distinguish aldehydes from ketones in the laboratory.
• Acidity and everyday importance — The chapter explains why carboxylic acids are markedly more acidic than alcohols and phenols and how substituents shift that acidity, then connects the whole family to real uses in flavours, perfumes, solvents, plastics and food preservation.

1. 01Aldehydes are more reactive than ketones in nucleophilic addition reactions due to both steric (one vs. two bulky substituents) and electronic (greater electrophilicity of carbonyl carbon) factors.
2. 02Aldehydes are distinguished from ketones using mild oxidising agents: Tollens' reagent gives a silver mirror with aldehydes; Fehling's reagent gives a reddish-brown precipitate (aromatic aldehydes do not respond to Fehling's test).
3. 03Aldehydes and ketones with at least one α-hydrogen undergo aldol condensation in dilute alkali to give β-hydroxy aldehydes or ketones; aldehydes without α-hydrogen undergo Cannizzaro reaction (disproportionation) with concentrated alkali.
4. 04Carboxylic acids are significantly more acidic than alcohols and phenols; electron-withdrawing substituents increase acidity by stabilising the carboxylate anion, while electron-donating groups decrease it.
5. 05Carboxylic acids are prepared by oxidation of primary alcohols and aldehydes, hydrolysis of nitriles and esters, treatment of Grignard reagents with CO2, and side-chain oxidation of alkylbenzenes.
6. 06Industrial uses span solvents (acetone, ethyl methyl ketone), food preservation (sodium benzoate), perfumery (benzaldehyde, vanillin), manufacture of nylon-6,6 (hexanedioic acid), and biological specimen preservation (formaldehyde/formalin).