Question

Which of the following reactions is shown by aldehydes that do not have alpha H-atom?

• A. Aldol condensation
• B. Cross aldol condensation
• C. Cannizzaro reaction
• D. Kolbe’s reaction

Answer 1

The Correct Option is C

Aldehydes without an alpha hydrogen undergo the Cannizzaro reaction in the presence of a base.

Answer 2

Aldehydes that lack an alpha hydrogen (hydrogens attached to the carbon adjacent to the carbonyl group) undergo the Cannizzaro reaction in the presence of a base. This reaction is a redox reaction where two molecules of the aldehyde react in the presence of a strong base to form an alcohol and a carboxylate ion.

In the Cannizzaro reaction, one molecule of the aldehyde undergoes reduction to form an alcohol, while the other molecule undergoes oxidation to form a carboxylate ion (the conjugate base of a carboxylic acid). This occurs due to the absence of a hydrogen atom on the alpha carbon, which prevents the typical aldol condensation from occurring. As a result, the reaction proceeds through a disproportionation mechanism.

An example of this reaction is the conversion of formaldehyde (HCHO) to methanol (CH₃OH) and formate ion (HCOO⁻), typically in the presence of a strong base such as sodium hydroxide (NaOH). The Cannizzaro reaction is particularly useful for synthesizing alcohols and carboxylates from aldehydes that cannot undergo aldol condensation due to the absence of alpha hydrogens.