Chemistry - STRUCTURAL ISOMERISM Question with Solution | TestHub

Keto-enol tautomerism needs an alpha hydrogen. (A) 3-methylbutan-2-one has alpha H on the methyl and on the methine carbon; (B) 2,6-dimethylcyclohexanone has alpha H at C-2 and C-6; (C) acetone has six alpha H. In (D), 2,2,6,6-tetramethylcyclohexanone, both alpha carbons (C-2 and C-6) are quaternary - they carry no hydrogen at all, so no enol can form. Hence (D).