Introduction:

In organic chemistry, the basicity of a compound refers to its ability to accept a proton (H+) and form a conjugate acid. Basicity is influenced by various factors such as electron density, resonance, inductive effects, and steric hindrance. In the case of p-methoxyaniline, p-chloroaniline, and p-methylaniline, the presence of different substituents on the aniline ring affects their basicity.

Effect of Electron-Donating Substituents:

1. p-Methoxyaniline:
- In p-methoxyaniline, the methoxy (-OCH3) group acts as an electron-donating substituent.
- The presence of this group increases the electron density on the aniline nitrogen atom through resonance and inductive effects.
- The lone pair of electrons on the nitrogen atom becomes more available for protonation, making p-methoxyaniline more basic.

2. p-Methylaniline:
- In p-methylaniline, the methyl (-CH3) group also acts as an electron-donating substituent.
- However, the electron-donating effect of the methyl group is weaker compared to the methoxy group.
- The electron density on the aniline nitrogen atom is slightly increased, making p-methylaniline less basic than p-methoxyaniline.

Effect of Electron-Withdrawing Substituents:

3. p-Chloroaniline:
- In p-chloroaniline, the chloro (-Cl) group acts as an electron-withdrawing substituent.
- The presence of this group decreases the electron density on the aniline nitrogen atom through resonance and inductive effects.
- The lone pair of electrons on the nitrogen atom becomes less available for protonation, making p-chloroaniline less basic compared to p-methoxyaniline.

Summary:

- p-Methoxyaniline is more basic than p-chloroaniline due to the electron-donating effect of the methoxy group.
- p-Methoxyaniline is less basic than p-methylaniline due to the stronger electron-donating effect of the methoxy group compared to the methyl group.
- p-Chloroaniline is less basic than p-methoxyaniline due to the electron-withdrawing effect of the chloro group.

In summary, the basicity of p-methoxyaniline is influenced by the electron-donating substituent, which increases the electron density on the aniline nitrogen atom, making it more basic than p-chloroaniline. However, p-methoxyaniline is less basic than p-methylaniline due to the weaker electron-donating effect of the methoxy group compared to the methyl group.