Which of the following aromatic or aliphatic compounds will completely FAIL to exhibit keto-enol tau — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Keto-enol tautomerism demands at least one $\alpha$ -hydrogen. Benzaldehyde lacks an $\alpha$ -hydrogen (the attached carbon is $sp^2$ and part of the phenyl ring). Benzophenone has two fully substituted phenyl rings attached to the carbonyl. 2,2-Dimethylpropanal features a fully blocked quaternary $sp^3$ $\alpha$ -carbon with zero attached hydrogens. Acetophenone, however, possesses a methyl group with three $\alpha$ -hydrogens, allowing it to easily tautomerize.