Selective Reduction of Ketone by NaBH4

Steps:

• Identify carvone's structure: α,β-unsaturated ketone with an isolated alkene.
• NaBH4 reduces the carbonyl (C=O) to a secondary alcohol (CH-OH).
• The conjugated double bond is not reduced under these conditions.
• The product retains the carbon skeleton and unsaturation, forming an allylic alcohol.

Why A is correct:

• A depicts the allylic alcohol from carbonyl reduction, matching NaBH4's selectivity for ketones over alkenes (hydride transfer to C=O, per nucleophilic addition mechanism).

Why the others are wrong:

• B likely shows full saturation, incorrect as NaBH4 ignores alkenes.
• C probably indicates epoxide or diol formation, wrong since NaBH4 doesn't perform those reactions.
• D may represent unreduced carvone or isomer, invalid as reduction occurs.

Final answer: A