Question

Arrange the following compounds in the increasing order of their reactivity towards HCN: 
I. Acetaldehyde 
II. Acetone 
III. Di-tert-butyl ketone

• A. II>I>II>IV>I
• B. II>I>IV>I>II
• C. IV>III>II>I
• D. II>IV>I>I>I

Hint:

Nucleophilic addition reactions are hindered by bulky groups around the carbonyl carbon, reducing the reactivity of ketones compared to aldehydes.

Answer 1

The Correct Option is C

The reactivity of aldehydes and ketones towards nucleophilic addition reactions is influenced by both steric and electronic effects. Acetaldehyde (I) is the most reactive because it has no bulky groups around the carbonyl group, making it easier for nucleophiles to approach and react with the carbonyl carbon. The absence of steric hindrance allows for faster nucleophilic attack.

Acetone (II) has a methyl group attached to the carbonyl group. While the methyl group is not particularly large, it still slightly reduces the reactivity compared to acetaldehyde because it introduces some electron-donating effects and creates minimal steric hindrance.

Di-tert-butyl ketone (III) has two large tert-butyl groups, which create significant steric hindrance around the carbonyl group. This large size of the substituents prevents nucleophiles from approaching the carbonyl carbon easily, making di-tert-butyl ketone the least reactive of the three compounds.

Therefore, the reactivity order is: I (acetaldehyde) > II (acetone) > III (di-tert-butyl ketone).