Selective Ketone Reduction by NaBH4

Steps:

• Carvone contains a ketone and an isolated alkene functional group.
• NaBH4 reduces ketones to secondary alcohols via hydride addition to the carbonyl carbon.
• The alkene remains unreduced, as NaBH4 does not affect C=C bonds under standard conditions.
• The product is thus the allylic alcohol from carbonyl reduction.

Why A is correct:

• A depicts the structure with the ketone reduced to -CH(OH)- and the alkene intact, matching NaBH4's selectivity for polar carbonyls over nonpolar alkenes.

Why the others are wrong:

• B shows only the alkene reduced, ignoring NaBH4's inability to hydrogenate C=C bonds.
• C shows both functional groups reduced, overestimating NaBH4's reactivity.
• D shows the unreduced carvone, failing to account for the ketone's reduction.

Final answer: A