Which one is the most acidic compound?

Options

A.
B.
C.
D.

Answer

To determine which compound is the most acidic among the given derivatives of phenol, we will analyze the effect of substituents on the acidity of phenol.

### Step-by-Step Solution:

1. **Understanding Acidity**:
- Acidity of a compound is influenced by the presence of electron-withdrawing or electron-donating groups. Electron-withdrawing groups (EWGs) increase acidity by stabilizing the negative charge on the conjugate base, while electron-donating groups (EDGs) decrease acidity by destabilizing the conjugate base.

2. **Analyzing the Compounds**:
- **Option A**: This compound has a methyl group (–CH3) attached to the phenol. The methyl group is an electron-donating group due to hyperconjugation, which increases electron density on the aromatic ring and decreases the acidity of phenol.

- **Option B**: This is simply phenol (C6H5OH). It has a moderate level of acidity as it does not have any substituents that significantly affect its acidity.

- **Option C**: This compound has a nitro group (–NO2) and a hydroxyl group (–OH). The nitro group is a strong electron-withdrawing group (–M effect), which increases the acidity of the compound by stabilizing the negative charge on the conjugate base.

- **Option D**: This compound has two nitro groups (–NO2) and a hydroxyl group (–OH). The presence of multiple nitro groups enhances the –M effect, leading to a greater stabilization of the negative charge on the conjugate base compared to Option C. Thus, this compound will be the most acidic.

3. **Conclusion**:
- After analyzing all options, we conclude that the compound with the most nitro groups (Option D) exhibits the highest acidity due to the cumulative –M effect of the nitro groups.

### Final Answer:
The most acidic compound is **Option D** (with three –NO2 groups).