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

Given: The reactivity of aldehydes and ketones in nucleophilic addition reactions is influenced by the electron-withdrawing or electron-donating effects of substituents attached to the aromatic ring or carbonyl group.

General Trend in Reactivity

- Electron-withdrawing groups (such as \( -NO_2 \)) attached to the aromatic ring increase the electrophilicity of the carbonyl carbon, thus increasing reactivity towards nucleophiles. - Electron-donating groups (such as \( -CH_3 \)) decrease the electrophilicity of the carbonyl carbon, decreasing reactivity towards nucleophiles.

Analysis of the Options

1. Benzaldehyde

- Benzaldehyde has no electron-donating or electron-withdrawing groups attached to the benzene ring. - It has moderate reactivity towards nucleophiles.

2. Acetophenone

- The \( -CH_3 \) group is an electron-donating group, which decreases the electrophilicity of the carbonyl carbon. - Therefore, acetophenone has lower reactivity compared to benzaldehyde.

3. p-Tolualdehyde

- The \( -CH_3 \) group is an electron-donating group, but less so than in acetophenone. - It lowers the electrophilicity of the carbonyl group but is more reactive than acetophenone.

4. p-Nitrobenzaldehyde

- The \( -NO_2 \) group is an electron-withdrawing group, which significantly increases the electrophilicity of the carbonyl carbon. - This makes p-nitrobenzaldehyde highly reactive towards nucleophiles.

Reactivity Order

Based on the electron-donating and electron-withdrawing effects of the substituents, the reactivity order is: \[ \text{Acetophenone} < \text{p-Tolualdehyde} < \text{Benzaldehyde} < \text{p-Nitrobenzaldehyde}. \]

Final Answer:

The correct answer is \( \boxed{(3)} \), which corresponds to **p-Tolualdehyde**.