Which of the following alkylbenzenes will undergo complete side-chain oxidation to form benzoic acid — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Side-chain oxidation of alkylbenzenes by strong oxidants like hot $KMnO_4$ relies on the presence of at least one benzylic $C-H$ bond. Regardless of the alkyl chain length, if a benzylic hydrogen is present, the entire side chain is cleaved and oxidized to a carboxylic acid group ($-COOH$). Toluene, ethylbenzene, and isopropylbenzene all possess benzylic hydrogens. $t$ -Butylbenzene lacks a benzylic hydrogen and is resistant to oxidation.