Which one of the following phenols will show highest acidity?

Options

A.
B.
C.
D.

Answer

To determine which phenol will show the highest acidity among the given options, we need to analyze the substituents attached to the phenolic ring and their effects on the stability of the phenoxide ion formed after the loss of a proton (H+).

### Step-by-Step Solution:

1. **Identify the Phenols**:
Let's assume we have four phenols with different substituents:
- Phenol A: OH and NO2 (nitro) at meta position and CH3 (methyl) at para position.
- Phenol B: OH and NO2 at para position.
- Phenol C: OH and NO2 at ortho position.
- Phenol D: OH and other substituents.

2. **Understand Acidity in Phenols**:
Acidity in phenols is influenced by the stability of the phenoxide ion (the conjugate base formed after losing H+). The more stable the phenoxide ion, the stronger the acid.

3. **Evaluate the Effects of Substituents**:
- **Electron-Withdrawing Groups (EWGs)**: Such as NO2, stabilize the negative charge on the phenoxide ion through resonance and inductive effects, thus increasing acidity.
- **Electron-Donating Groups (EDGs)**: Such as CH3, destabilize the negative charge, thus decreasing acidity.

4. **Analyze Each Phenol**:
- **Phenol A**: The CH3 group is an EDG (it donates electron density) and is at the para position, while the NO2 group is at the meta position and acts as an EWG. The overall effect is destabilizing due to the presence of the CH3 group.
- **Phenol B**: The NO2 group is at the para position, which strongly withdraws electrons and stabilizes the phenoxide ion. This phenol is likely to be more acidic than Phenol A.
- **Phenol C**: The NO2 group is at the ortho position, which provides strong stabilization through resonance (strong -M effect). This makes the phenoxide ion more stable and thus increases acidity significantly.
- **Phenol D**: The effects of substituents need to be evaluated similarly, but if it has EDGs, it will likely be less acidic.

5. **Conclusion**:
Based on the analysis, Phenol C, which has the NO2 group at the ortho position, will show the highest acidity. The ortho position allows for effective resonance stabilization of the phenoxide ion, making it the most acidic among the options.

### Final Answer:
**Phenol C (with NO2 at the ortho position) will show the highest acidity.**