Question

Which of the following statement(s) is/are true about the benzoin reaction ?

• A. $C{N}^{\ominus }$ attacks at the $(C=O)$ group of (A).
• B. $C{N}^{\ominus }$ attacks at $(C=O)$ group of (B).
• C. The major product formed is :
• D. The major product formed is :

Answer 1

Answer: (A), (C)

The major product formed is :

Aromatioc aldehyde reacts with alcoholic KCN to form benzoin product. This reaction is called Benzoin reaction.

Mechanism of Benzoin reaction:
1. Nucleophilic addition of $C{N}^{-}$: $C{N}^{-}$ will attack the more electrophilic carbonyl carbon and charge reversibility take place between O and C to give carbanion which is called umpolung reaction.
2. Nucleophilic addition of carbanion: Formed carbanion will attack the electrophilic carbon of other aldehyde followed by proton abstraction which leads to removal of cyanide ion.

Among A and B, (A) has more electrophilic carbonyl carbon due to electron withdrawing nature of nitro group so $C{N}^{-}$ will attack here.


Hence, the correct answers are A and C