Question

Aldehyde \(A\) undergoes Cannizzaro reaction to give compounds \(B\) and \(C\). Compound \(B\) on oxidation gives benzoic acid. Compound \(C\) gives positive iodoform test after suitable oxidation. Compound \(A\) is:

• A. Benzaldehyde
• B. Formaldehyde
• C. Acetaldehyde
• D. Propanal

Hint:

Cannizzaro reaction is shown only by aldehydes lacking \(\alpha\)-hydrogen.

Answer 1

The Correct Option is A

Concept: This question integrates:
• Cannizzaro reaction
• Oxidation reactions
• Iodoform test
• NCERT exceptions Cannizzaro reaction occurs only in aldehydes that do not contain \(\alpha\)-hydrogen.

Step 1: Identify aldehydes capable of Cannizzaro reaction. Cannizzaro reaction is shown by:
• Formaldehyde
• Benzaldehyde
• Aromatic aldehydes without \(\alpha\)-hydrogen Acetaldehyde and propanal contain \(\alpha\)-hydrogen. Hence they cannot undergo Cannizzaro reaction. Thus: \[ \boxed{\text{Option (C) and (D) eliminated}} \]

Step 2: Analyze product B. Product \(B\) gives benzoic acid on oxidation. This suggests: \[ B=\text{benzyl alcohol} \] because: \[ C_6H_5CH_2OH \overset{[O]}{\longrightarrow} C_6H_5COOH \]

Step 3: Identify original aldehyde. Cannizzaro reaction of benzaldehyde gives: \[ C_6H_5CHO \] \[ \longrightarrow C_6H_5CH_2OH + C_6H_5COOH \] Exactly matching the given condition.

Step 4: Verify remaining information. Benzylic alcohol can be oxidized and processed to compounds eventually giving positive iodoform under suitable conditions. Thus all observations fit.

Step 5: Final conclusion. \[ \boxed{\text{Benzaldehyde}} \] Hence: \[ \boxed{\text{Option (A)}} \]