Which of the following is most acidic :

Options

A. Phenol
B. Benzyl alcohol
C. m-chlorophenol
D. cyclohexanol

Answer

To determine which of the given compounds is the most acidic, we will analyze the acidity of each compound step by step.

### Step 1: Identify the Compounds
We have the following compounds to analyze:
1. Phenol
2. Benzyl alcohol
3. Metachlorophenol
4. Cyclohexanol

### Step 2: Understand Acidity
Acidity in organic compounds is often influenced by the stability of the conjugate base formed after deprotonation (removal of a hydrogen ion, H⁺). The more stable the conjugate base, the stronger the acid.

### Step 3: Analyze Each Compound
- **Phenol (C6H5OH)**: When phenol loses a proton, it forms the phenoxide ion (C6H5O⁻). The negative charge is delocalized over the aromatic ring, which stabilizes the conjugate base.

- **Benzyl Alcohol (C6H5CH2OH)**: When benzyl alcohol loses a proton, it forms the benzyl oxide ion (C6H5CH2O⁻). The negative charge is localized on the oxygen and is not stabilized by resonance with the aromatic ring as effectively as in phenol.

- **Metachlorophenol**: The presence of the chlorine atom in the meta position can influence acidity. Chlorine is an electronegative atom that can withdraw electron density through the inductive effect, stabilizing the conjugate base (metachlorophenoxide) more than in phenol.

- **Cyclohexanol (C6H11OH)**: Cyclohexanol does not have any resonance stabilization for its conjugate base (cyclohexoxide). The alkyl groups provide a +I (inductive) effect, which increases electron density on the oxygen, making it less acidic.

### Step 4: Compare Acidity
- **Cyclohexanol** is the least acidic due to lack of resonance stabilization and the +I effect from alkyl groups.
- **Benzyl alcohol** is more acidic than cyclohexanol but less acidic than phenol due to the lack of resonance stabilization.
- **Phenol** is more acidic than both cyclohexanol and benzyl alcohol because of resonance stabilization of the phenoxide ion.
- **Metachlorophenol** is the most acidic because the chlorine atom withdraws electron density, stabilizing the conjugate base even more than in phenol.

### Conclusion
Based on the analysis, **Metachlorophenol** is the most acidic compound among the given options.