Question

Which of the following arrangements with respect to their reactivity in nucleophilic addition reaction is correct?

• A. benzaldehyde \(<\) acetophenone \(<\) p-nitrobenzaldehyde \(<\) p-tolualdehyde
• B. acetophenone \(<\) benzaldehyde \(<\) p-tolualdehyde \(<\) p-nitrobenzaldehyde
• C. acetophenone \(<\) p-tolualdehyde \(<\) benzaldehyde \(<\) p-nitrobenzaldehyde
• D. p-nitrobenzaldehyde \(<\) benzaldehyde \(<\) p-tolualdehyde \(<\) acetophenone

Hint:

In nucleophilic addition reactions, electron-withdrawing groups increase the reactivity of carbonyl compounds, while electron-donating groups decrease their reactivity. This principle is crucial in determining the reactivity order of different compounds.

Answer 1

The Correct Option is C

This query concerns the comparative reactivity of various carbonyl compounds in nucleophilic addition reactions. Predicting reaction outcomes necessitates an understanding of the electronic and steric factors influencing reactivity.

The reactivity order of carbonyl compounds in nucleophilic addition is primarily governed by:

• Electronic effects: Electrophilic character of the carbonyl carbon is amplified by electron-withdrawing groups, thus increasing reactivity.
• Steric effects: Greater accessibility of the carbonyl carbon to nucleophiles, facilitated by smaller substituents, enhances reactivity.

An examination of each compound follows:

1. Acetophenone: The phenyl group, through resonance, donates electrons, reducing the carbonyl carbon's electrophilicity. The phenyl group's size also introduces steric hindrance, diminishing reactivity.
2. p-Tolualdehyde: The methyl group is a mild electron donor. However, the carbonyl group is more accessible than in acetophenone, resulting in higher reactivity.
3. Benzaldehyde: Lacking the steric bulk of acetophenone and electron-donating groups, benzaldehyde exhibits greater reactivity than both acetophenone and p-tolualdehyde.
4. p-Nitrobenzaldehyde: The presence of a potent electron-withdrawing nitro group significantly increases the carbonyl carbon's electrophilicity, rendering it the most reactive compound among those listed.

Consequently, the established order of reactivity for nucleophilic addition reactions is:

\(\text{acetophenone} < \text{p-tolualdehyde} < \text{benzaldehyde} < \text{p-nitrobenzaldehyde}\)

This aligns with the provided correct option:

acetophenone < p-tolualdehyde < benzaldehyde < p-nitrobenzaldehyde