Question

An optically active compound A, C6H10O2, when dissolved in NaOH solution, consumed one equivalent of base. On acidification, compound A was slowly regenerated. Treatment of A with LiAlH4 in ether followed by protonolysis gave an optically inactive compound B that reacted with acetic anhydride to give an acetate diester derivative C. Compound B was oxidized by aqueous chromic acid to ?-methylglutaric acid (3-methylpentanedioic acid), D. Identify compounds A, B, and C; do not specify stereochemistry. (The absolute stereochemical configurations of chiral substances cannot be determined from the data.)

Answer 1

Compound A has only two oxygen atoms. It reacts with one equivalent of NaOH and regenerates on acidification. It reacts with LAH to give a compound having two hydroxyl groups as it forms diacetate on reaction with acetic anhydride. All the above observations suggest that compound A is a lactone.

Compound B obtained by LAH reduction of compound A on chromic acid oxidation gives 3-methylpentanedioic acid, thus structure of compound A and B can be suggested as given in the above scheme.