Which of the following is the least basic?

Options

A.
B.
C.
D. All are equally basic

Answer

To determine which of the given compounds is the least basic, we need to analyze the basicity of each compound based on the substituents attached to the aniline moiety. Basicity in amines is influenced by the ability of the nitrogen atom to donate its lone pair of electrons, which can be affected by electron-withdrawing or electron-donating groups.

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's assume we have the following compounds based on the video transcript:
- Compound A: Nitroaniline (with -NO2 group)
- Compound B: Methoxyaniline (with -OCH3 group)
- Compound C: Aniline with another benzene ring (diphenylamine)

2. **Understand Basicity**:
Basicity is the ability of a compound to donate a lone pair of electrons. The presence of electron-withdrawing groups decreases basicity, while electron-donating groups increase it.

3. **Analyze Compound A (Nitroaniline)**:
- The -NO2 group is a strong electron-withdrawing group due to its -I (inductive) and -M (mesomeric) effects.
- This reduces the electron density on the nitrogen atom, making it less likely to donate its lone pair.
- Therefore, Nitroaniline is expected to have low basicity.

4. **Analyze Compound B (Methoxyaniline)**:
- The -OCH3 group has a +M effect (it donates electron density through resonance) and a -I effect (it withdraws electron density inductively).
- The +M effect increases the electron density on the nitrogen atom, enhancing its ability to donate the lone pair.
- Thus, Methoxyaniline is more basic than Nitroaniline.

5. **Analyze Compound C (Diphenylamine)**:
- The presence of another benzene ring can delocalize the lone pair of electrons on the nitrogen atom through resonance.
- This delocalization reduces the availability of the lone pair for donation, thus decreasing its basicity.
- However, it is still less affected than Nitroaniline.

6. **Conclusion**:
- Comparing the basicity of the three compounds, Nitroaniline (Compound A) has the least basicity due to the strong electron-withdrawing effect of the -NO2 group.
- Therefore, the correct answer is **Compound A: Nitroaniline**.