In each of the following pair of compounds, which is more basic in aqueous solution? Give an explanation for your choice:
m-nitroaniline or p-nitroaniline

Answer

To determine which compound is more basic in aqueous solution between m-nitroaniline and p-nitroaniline, we need to analyze the effects of the nitro group on the basicity of the aniline derivatives.

### Step-by-Step Solution:

1. **Understanding Basicity**:
Basicity refers to the ability of a compound to donate a lone pair of electrons. In the context of aniline derivatives, the nitrogen atom in the amine group (–NH2) is the site that donates the lone pair.

2. **Analyzing the Position of the Nitro Group**:
- **m-Nitroaniline**: The nitro group is in the meta position relative to the amine group.
- **p-Nitroaniline**: The nitro group is in the para position relative to the amine group.

3. **Effect of the Nitro Group**:
The nitro group (-NO2) is a strong electron-withdrawing group due to its -I (inductive) and -M (mesomeric) effects.
- In **p-nitroaniline**, the nitro group can participate in resonance with the amine group. This resonance delocalizes the lone pair of electrons on the nitrogen, making it less available for donation, thus reducing the basicity.
- In **m-nitroaniline**, the nitro group does not have a resonance effect on the nitrogen lone pair because it is positioned meta to the amine group. The electron-withdrawing inductive effect is present, but it is less significant compared to the resonance effect seen in the para position.

4. **Comparing Basicity**:
Since the resonance effect in p-nitroaniline significantly reduces the availability of the nitrogen's lone pair for donation, while in m-nitroaniline, the lone pair remains more available, we can conclude that:
- **m-Nitroaniline is more basic than p-nitroaniline**.

### Conclusion:
m-Nitroaniline is more basic in aqueous solution than p-nitroaniline due to the lack of resonance stabilization of the nitrogen lone pair in the meta position, allowing for greater availability of the lone pair for donation.

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