Which of the following is most acidic ?

Options

A. Benzyl alcohol
B. Cyclohexanol
C. Phenol
D. m-Chlorophenol

Answer

To determine which of the given compounds is the most acidic, we need to analyze the stability of the conjugate bases formed when each compound donates a proton (H+). The more stable the conjugate base, the stronger the acid.

### Step-by-Step Solution:

1. **Identify the Compounds**:
Let's denote the compounds as follows:
- A: Benzyl Alcohol
- B: Cyclohexanol
- C: Phenol
- D: Chlorophenol (Meta)

2. **Understanding Acidity**:
An acid (HA) donates a proton (H+) to form its conjugate base (A-). The acidity of the acid depends on the stability of the conjugate base. The more stable the conjugate base, the stronger the acid.

3. **Analyze Each Compound**:
- **Benzyl Alcohol (A)**: When it loses H+, it forms a conjugate base that has a negative charge on the oxygen. The stability of this conjugate base is decreased due to the increase in electron density in the aromatic ring.

- **Cyclohexanol (B)**: Similar to benzyl alcohol, when it loses H+, it forms a conjugate base with a negative charge on the oxygen. However, cyclohexanol does not have any resonance stabilization, making it a weaker acid compared to phenol.

- **Phenol (C)**: Upon losing H+, phenol forms a conjugate base that can stabilize the negative charge through resonance with the aromatic ring. This delocalization of charge increases the stability of the conjugate base, making phenol a stronger acid.

- **Chlorophenol (D)**: The chlorophenol also forms a conjugate base that can stabilize the negative charge through resonance. Additionally, the chlorine atom is an electron-withdrawing group, which further stabilizes the negative charge on the conjugate base by decreasing electron density.

4. **Comparing Stability**:
- **Benzyl Alcohol**: Less stable due to increased electron density.
- **Cyclohexanol**: Least stable as it lacks resonance stabilization.
- **Phenol**: Moderately stable due to resonance.
- **Chlorophenol**: Most stable due to resonance and the electron-withdrawing effect of chlorine.

5. **Conclusion**:
Based on the stability of the conjugate bases, chlorophenol (D) is the most acidic compound among the options provided.

### Final Answer:
**Chlorophenol (D) is the most acidic.**