Question

Which of the following compounds would undergo aldol condensation, which undergoe Cannizzaro reaction and which neither? Write the structures of the expected products of aldol condensation and Cannizzaro reaction.

(i) Methanal
(ii) 2-Methylpentanal
(iii) Benzaldehyde
(iv) Benzophenone
(v) Cyclohexanone
(vi) 1-Phenylpropanone
(vii) Phenylacetaldehyde
(viii) Butan-1-ol
(ix) 2,2-Dimethylbutanal

Answer 1

(i) Methanal: Cannizzaro (Methanol and Formic Acid)

(ii) 2-Methylpentanal: Aldol (β-Hydroxy Ketone)

(iii) Benzaldehyde: Aldol (β-Hydroxy Ketone)

(iv) Benzophenone: Neither

(v) Cyclohexanone: Neither

(vi) 1-Phenylpropanone: Aldol (β-Hydroxy Ketone)

(vii) Phenylacetaldehyde: Cannizzaro (Benzyl Alcohol and Benzoic Acid)

(viii) Butan-1-ol: Neither

(ix) 2,2-Dimethylbutanal: Cannizzaro (2,2-Dimethylbutanol and 2,2-Dimethylbutanoic Acid) .

Aldol Condensation and Cannizzaro Reaction are two different types of reactions that involve carbonyl compounds.

Aldol condensation typically occurs between two molecules of an aldehyde or ketone, resulting in the formation of a β-hydroxy carbonyl compound (aldol).

The reaction involves the nucleophilic addition of an enolate ion to the carbonyl group of another molecule.

Cannizzaro Reaction:

The Cannizzaro reaction involves the disproportionation of an aldehyde into an alcohol and a carboxylic acid.

It usually occurs when there is no alpha-hydrogen in the aldehyde.

Now let's consider each compound:

(i) Methanal: Undergoes Cannizzaro reaction. No alpha-hydrogens for aldol condensation. The products would be methanol and formic acid.

(ii) 2-Methylpentanal: Undergoes aldol condensation. The product would be a β-hydroxy ketone.

(iii) Benzaldehyde: Undergoes aldol condensation. The product would be a β-hydroxy ketone.

(iv) Benzophenone: Neither aldol condensation nor Cannizzaro reaction as it lacks alpha-hydrogens.

(v) Cyclohexanone: Neither aldol condensation nor Cannizzaro reaction as it lacks alpha-hydrogens.

(vi) 1-Phenylpropanone: Undergoes aldol condensation. The product would be a β-hydroxy ketone.

(vii) Phenylacetaldehyde: Undergoes Cannizzaro reaction. No alpha-hydrogens for aldol condensation. The products would be benzyl alcohol and benzoic acid.

(viii) Butan-1-ol: Neither aldol condensation nor Cannizzaro reaction as it is an alcohol.

(ix) 2,2-Dimethylbutanal: Undergoes Cannizzaro reaction. No alpha-hydrogens for aldol condensation. The products would be 2,2-dimethylbutanol and 2,2-dimethylbutanoic acid.