Question

Which of the following gives Cannizzaro's reaction?

• A. \(\mathrm{CH_3CHO}\)
• B. \(\mathrm{HCHO}\)
• C. \(\mathrm{HCOOH}\)
• D. \(\mathrm{CH_3COCH_3}\)

Hint:

Aldehydes without \(\alpha\)-H (e.g., formaldehyde, benzaldehyde) give Cannizzaro; those with \(\alpha\)-H prefer aldol condensation.

Answer 1

The Correct Option is B

Step 1: Condition for Cannizzaro reaction.
It occurs with aldehydes that lack \(\alpha\)-hydrogen. Such aldehydes undergo self-oxidation and self-reduction in strong base to give a salt of a carboxylic acid and an alcohol.
Step 2: Check options for \(\alpha\)-H.
(A) \(\mathrm{CH_3CHO}\): has \(\alpha\)-H \(\Rightarrow\) gives aldol, not Cannizzaro.
(B) \(\mathrm{HCHO}\) (formaldehyde): has no \(\alpha\)-H \(\Rightarrow\) undergoes Cannizzaro.
(C) \(\mathrm{HCOOH}\): not an aldehyde (it is a carboxylic acid).
(D) \(\mathrm{CH_3COCH_3}\): a ketone; does not show Cannizzaro.
Step 3: Conclusion.
Thus, \(\mathrm{HCHO}\) is the correct choice \(\Rightarrow\) (B).