Aldehydes, Ketones and Carboxylic Acids — Class 12 Chemistry

This unit deals with organic compounds containing the carbonyl group (>C=O) and the carboxyl group (-COOH). In aldehydes the carbonyl carbon is bonded to at least one hydrogen, in ketones it is bonded to two carbon atoms, and in carboxylic acids the carbon bears a hydroxyl as well, giving -COOH. These compounds are named by common and IUPAC systems. Aldehydes and ketones are prepared by oxidation of alcohols, ozonolysis of alkenes, hydration of alkynes and from acid derivatives; carboxylic acids are prepared by oxidation of primary alcohols and aldehydes, and from nitriles, Grignard reagents and acyl derivatives. The carbonyl carbon, being electron deficient, is attacked by nucleophiles, so aldehydes and ketones undergo nucleophilic addition reactions (with HCN, alcohols, ammonia derivatives) and the alpha-hydrogen makes them acidic enough for aldol and related condensations; aldehydes are more reactive and are readily oxidised, distinguishing them from ketones by Tollens' and Fehling's tests. Carboxylic acids are appreciably acidic because the carboxylate ion is resonance stabilised, and electron-withdrawing groups increase the acidity. They form salts, esters, anhydrides, acid chlorides and amides. These carbonyl and carboxyl compounds are constituents of perfumes, plastics, dyes, drugs and many foods.