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The products formed in the following reaction, A and B are A compound containing a cyclohexanone ring with a formyl substituent (–CHO) on the bottom carbon is treated with [Ag(NH3)2]+ / OH− to give A, and then A is treated with NaBH4 to give B.

1. A is cyclohexanone with the –CHO group converted to –CH2OH; B is the corresponding alcohol with the ring carbonyl reduced to –OH and the side chain remaining –CH2OH
2. A is cyclohexanone with the –CHO group converted to –COOH; B is the corresponding alcohol with the ring carbonyl reduced to –OH and the side chain remaining –CH2OH
3. A is cyclohexanone with the –CHO group converted to –COOH; B is the corresponding alcohol with the ring carbonyl reduced to –OH and the side chain remaining –COOH
4. A is cyclohexanone with the –CHO group converted to –COOH; B is the corresponding alcohol with the ring carbonyl reduced to –OH and the side chain remaining –CH2OH

Correct answer: A is cyclohexanone with the –CHO group converted to –COOH; B is the corresponding alcohol with the ring carbonyl reduced to –OH and the side chain remaining –COOH

Solution

Tollens reagent [Ag(NH3)2]+/OH- selectively oxidizes the aldehyde (-CHO) to -COOH, leaving the ring ketone unchanged (A = ring ketone + -COOH). NaBH4 then reduces only the ketone to -OH and does NOT reduce the carboxylic acid, so B has the ring -OH and the side chain still -COOH.

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