Question

Through which of the following reactions can the number of carbon atoms be increased in the chain?

(i) Grignard reaction

(ii) Cannizzaro’s reaction

(iii) Aldol condensation

(iv) HVZ reaction

• A. i, ii
• B. ii, iii
• C. iii, iv
• D. i, iii

Answer 1

Correct option: (D)
(i) Grignard reagent has carbon nucleophile $\left(R^{-}\right)$ which can add to electrophilic carbon centres and increase the length of the carbon chain.

Example: Reaction of acetone with Grignard reagent

(ii) Cannizzaro's reaction is all about the disproportionation of non-enolized aldehydes (aldehyde having no $\alpha$-H) into corresponding alcohols and acids. Hence it will not increase the chain.

Example: Cannizaro reaction of Benzaldehyde

(iii) Aldol reaction involves the reaction of enolate with a carbonyl to produce a conjugated enone. It increases the carbon chain length.

Example: Aldol condensation of benzaldehyde and acetophenone

(iv) In the HVZ reaction, an acid gets halogenated at its alpha position. Since no carbon nucleophile is involved hence it is not going to increase the length of the carbon chain.

Example:

Hence, the correct option is (D).