The minimum value of `-logK_(b)` will be for the compound

Options

A. o - Nitroaniline
B. p - Nitroaniline
C. p - Chloroaniline
D. p - Methoxyaniline

Answer

To find the minimum value of \(-\log K_b\) for the given compounds, we need to analyze the basicity of the amines provided. The basicity of an amine is influenced by the substituents attached to the aromatic ring, particularly how they affect the lone pair of electrons on the nitrogen atom.

### Step-by-Step Solution:

1. **Understanding the Relationship**:
- Recall that \(K_b\) is the base dissociation constant, and \(-\log K_b\) is referred to as \(pK_b\).
- A lower \(pK_b\) value indicates a stronger base, which corresponds to a higher \(K_b\) value.

2. **Identify the Compounds**:
- The compounds given are:
- Ortho Nitro Aniline
- Para Nitro Aniline
- Para Chloro Aniline
- Methoxy Aniline

3. **Analyze Each Compound**:
- **Ortho Nitro Aniline**: The nitro group (-NO2) is an electron-withdrawing group, which decreases the electron density on the nitrogen atom, making it less basic.
- **Para Nitro Aniline**: Similar to ortho, the nitro group withdraws electron density from the nitrogen, decreasing its basicity.
- **Para Chloro Aniline**: The chloro group (-Cl) is also an electron-withdrawing group, but it is less effective than nitro in resonance. This compound will have moderate basicity.
- **Methoxy Aniline**: The methoxy group (-OCH3) is an electron-donating group through resonance, which increases the electron density on the nitrogen atom, making it more basic.

4. **Determine Basicity Order**:
- Based on the analysis:
- Methoxy Aniline > Para Chloro Aniline > Para Nitro Aniline > Ortho Nitro Aniline
- Therefore, Methoxy Aniline is the most basic among the given compounds.

5. **Conclusion**:
- Since Methoxy Aniline has the highest basicity, it will correspond to the minimum value of \(-\log K_b\).
- Thus, the minimum value of \(-\log K_b\) will be for Methoxy Aniline.

### Final Answer:
The minimum value of \(-\log K_b\) will be for Methoxy Aniline.