Question

Among H—CHO, CH\(_3\)CHO and C\(_6\)H\(_5\)CHO, which will undergo Cannizzaro's reaction?

• A. HCHO and CH\(_3\)CHO
• B. CH\(_3\)CHO and C\(_6\)H\(_5\)CHO
• C. C\(_6\)H\(_5\)CHO and HCHO
• D. All of the above

Hint:

Aldehydes without \(\alpha\)-hydrogen undergo Cannizzaro reaction.

Answer 1

The Correct Option is C

The Cannizzaro reaction is a redox reaction where two molecules of an aldehyde react to produce a primary alcohol and a carboxylic acid in the presence of a base. This reaction only occurs with aldehydes that do not have an alpha hydrogen atom. Let's analyze the given compounds:

1. HCHO (Formaldehyde):
   • Formaldehyde has the structure HCHO.
   • It does not contain any alpha hydrogen (a hydrogen atom attached to the carbon adjacent to the carbonyl group).
   • Therefore, it can participate in the Cannizzaro reaction.
2. CH₃CHO (Acetaldehyde):
   • The structure of acetaldehyde is CH₃CHO.
   • It has three alpha hydrogens (attached to the carbon bearing the CH₃ group).
   • Because it has alpha hydrogen atoms, it cannot undergo the Cannizzaro reaction but rather favors Aldol condensation.
3. C₆H₅CHO (Benzaldehyde):
   • Benzaldehyde has the structure C₆H₅CHO.
   • There are no alpha hydrogens in benzaldehyde since the alpha carbon is part of the aromatic ring structure.
   • Thus, benzaldehyde can participate in the Cannizzaro reaction.

Based on the analysis:

• \(HCHO\) and \(C_{6}H_{5}CHO\) can undergo Cannizzaro's reaction because both lack alpha hydrogen atoms.
• \(CH_{3}CHO\) cannot undergo Cannizzaro's reaction because it has alpha hydrogen atoms.

Therefore, the correct answer is C₆H₅CHO and HCHO.