In which of the following molecules, the substituent does not exert it's resonance effect ?

Options

A. `C_6H_5NH_2`
B. `C_6H_5NH_3^(o+)`
C. `C_6H_5_OH`
D. `C_6H_5Cl`

Answer

To determine which substituent does not exert its resonance effect in the given molecules, we need to analyze the substituents attached to the benzene ring in each option.

### Step-by-Step Solution:

1. **Identify the Molecules**:
We have several molecules with a benzene ring and different substituents. Let's denote them as:
- Option A: Substituent 1
- Option B: Substituent 2 (NH3 with a positive charge)
- Option C: Substituent 3 (Alcohol)
- Option D: Substituent 4 (Chlorine)

2. **Understand Resonance**:
Resonance occurs when there is a delocalization of electrons through π bonds or lone pairs. For a substituent to exert a resonance effect, it typically needs to have a lone pair of electrons that can participate in the resonance.

3. **Analyze Each Substituent**:
- **Substituent 1**: (Assuming it has a lone pair) This could potentially exert resonance.
- **Substituent 2 (NH3 with a positive charge)**: The nitrogen in NH3 has no lone pair available for resonance due to the positive charge. Therefore, it cannot participate in resonance.
- **Substituent 3 (Alcohol)**: The oxygen in the alcohol has lone pairs that can participate in resonance.
- **Substituent 4 (Chlorine)**: Chlorine has lone pairs that can also participate in resonance.

4. **Conclusion**:
After analyzing the substituents, we find that the substituent that does not exert its resonance effect is **Substituent 2 (NH3 with a positive charge)**. This is because the positive charge on nitrogen means it does not have a lone pair to contribute to resonance.

### Final Answer:
The substituent that does not exert its resonance effect is **NH3 with a positive charge**.