Question

Aldehydes are more reactive than ketone towards nucleophilic attack because of?

• A. less steric hindrance in ketone
• B. presence of two alkyl group on ketone decreases its electrophilicity
• C. presence of one alkyl group on aldehyde decreases its electrophilicity
• D. alkyl group have electron withdrawing effect.

Hint:

Alkyl groups donate electrons and crowd the carbonyl carbon.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Nucleophilic addition begins when a nucleophile attacks the partly positive carbonyl carbon. The more positive that carbon, and the less crowded it is, the faster the reaction.

Step 2: Aldehyde versus ketone:
An aldehyde has one alkyl group and one H on the carbonyl carbon. A ketone has two alkyl groups. Alkyl groups push electrons (+I effect) towards the carbon, which lowers its positive charge. Two alkyl groups push more than one, so a ketone carbon is less electrophilic.

Step 3: Check the options:
(A) wrongly says there is less hindrance in ketone, but ketones have more hindrance. (C) wrongly says one alkyl group on aldehyde decreases electrophilicity, while this is the smaller effect. (D) alkyl groups donate electrons, they are not withdrawing. So (B) is the reason.

Final Answer:
Two alkyl groups on a ketone reduce the electrophilicity of its carbonyl carbon. \[ \boxed{B} \]