Which among the following compounds has highest order of reactivity in nucleophilic addition reaction?

Question

Accepted Answer

Option 3, p-nitrobenzaldehyde, is the correct answer for having the highest order of reactivity in nucleophilic addition reactions. Here's why:

1. **Explanation for Option 3 (p-nitrobenzaldehyde):**
   - p-Nitrobenzaldehyde contains a nitro group (-NO2) attached to the benzene ring. The nitro group is a strong electron-withdrawing group due to its resonance and inductive effects. This electron-withdrawing nature increases the positive character of the carbonyl carbon in the aldehyde group, making it more susceptible to attack by nucleophiles. The increased electrophilicity of the carbonyl carbon enhances the reactivity of p-nitrobenzaldehyde in nucleophilic addition reactions.

2. **Explanation for why other options are incorrect:**

- **Option 1 (Benzaldehyde):**
     - Benzaldehyde lacks any additional electron-withdrawing groups that could enhance the electrophilicity of the carbonyl carbon. While it is reactive in nucleophilic addition reactions, it is less reactive compared to p-nitrobenzaldehyde because it does not have the additional electron-withdrawing effect provided by a nitro group.

- **Option 2 (p-tolualdehyde):**
     - p-Tolualdehyde has a methyl group (-CH3) attached to the benzene ring, which is an electron-donating group. This group decreases the electrophilicity of the carbonyl carbon by donating electron density through hyperconjugation and inductive effects. As a result, p-tolualdehyde is less reactive in nucleophilic addition reactions compared to p-nitrobenzaldehyde.

- **Option 4 (Acetophenone):**
     - Acetophenone is a ketone, and ketones are generally less reactive in nucleophilic addition reactions compared to aldehydes due to steric hindrance and the electron-donating effect of the alkyl group attached to the carbonyl carbon. Additionally, acetophenone does not have an electron-withdrawing group like the nitro group in p-nitrobenzaldehyde, making it less reactive.

In conclusion, the presence of the strong electron-withdrawing nitro group in p-nitrobenzaldehyde significantly enhances its reactivity in nucleophilic addition reactions, making it the most reactive compound among the given options.