Question

In Claisen condensation reaction (when an ester is treated with a strong base) :

• A. A proton is removed from the $\alpha$ -carbon to form a resonance stabilised carbanion of the ester
• B. Carbanion acts as a nucleophile in a nucleophilic acyl substitution reaction with another ester molecule
• C. A new $C-C$ bond is formed.
• D. $\alpha ,\beta$ unsaturated product is obtained

Answer 1

Answer: (A), (B), (C)

A new $C-C$ bond is formed.

Ester undergoes self condensation in presence of strong base to give $\beta$-ketoester. This reaction is called Claisen condensation reaction.


Mechanism of Claisen condensation reaction:
1. Enolate formation : The strong base will abstract the acidic $\alpha$-hydrogen to form the enolate ion which is in resonance with the ester group.

2. Nucleophile attack: Formed enolate will attack the carbonyl carbon of another ester molecule and leaving group (-OR) will leave the compound to form $\beta -$ ketoester. The reaction leads to new $C-C$ bond between the two ester substrate.

Hence, option (a), (b) and (c) are correct.