Arrange the following compounds in increasing order towards Nucleophi…

The correct answer is Option (1) → (D), (C), (B), (A)

Core Concept:

Nucleophilic addition reactions occur at the carbonyl carbon. The reactivity depends mainly on two factors:

Steric hindrance

Electron donating or withdrawing effects

More bulky groups reduce reactivity

Aldehydes are more reactive than ketones

Aromatic rings decrease reactivity due to resonance

Option-wise explanation:

Option A Propanal

Propanal is an aliphatic aldehyde. It has one alkyl group and one hydrogen attached to the carbonyl carbon. Hydrogen causes very little steric hindrance and alkyl groups donate electrons only slightly. Thus the carbonyl carbon remains highly electrophilic. Hence propanal shows high nucleophilic addition reactivity.

Option B Benzaldehyde

Benzaldehyde is an aromatic aldehyde. The benzene ring donates electrons through resonance to the carbonyl group. This reduces the positive character of the carbonyl carbon. Therefore nucleophilic attack becomes harder compared to aliphatic aldehydes.

Option C Acetone

Acetone is a ketone with two alkyl groups attached. Alkyl groups donate electrons by +I effect and reduce electrophilicity. Hence acetone is less reactive than aldehydes.

Option D Di-tert-butyl ketone

This ketone has two tert-butyl groups which are very bulky. They create severe steric hindrance around the carbonyl carbon. This makes nucleophilic attack extremely difficult. Therefore it shows the least reactivity.