Question

Which of the following is most acidic?

• A. \( \text{Benzyl alcohol} \)
• B. \( \text{Cyclohexanol} \)
• C. \( \text{Phenol} \)
• D. \( m\text{-chlorophenol} \)

Hint:

Electron-withdrawing groups like -Cl increase the acidity of phenols by stabilizing the phenoxide ion through resonance, making the compound more prone to losing a proton.

Answer 1

The Correct Option is D

Phenols exhibit greater acidity compared to alcohols due to the resonance stabilization of the phenoxide ion formed after losing a proton (\( \text{H}^+ \)). This resonance delocalizes the negative charge on the oxygen, enhancing the compound's acidity. Electron-withdrawing substituents, such as -Cl, further increase the acidity of phenols by stabilizing the negative charge on the oxygen atom. Step 1: Structure comparison.
Benzyl alcohol: Less acidic, as the hydroxyl group is attached to a saturated carbon, and there is no resonance stabilization.
Cyclohexanol: Similar to benzyl alcohol, it lacks resonance stabilization and is therefore less acidic.
Phenol: More acidic due to the resonance stabilization of the phenoxide ion.
m-Chlorophenol: The most acidic, as the -Cl group is an electron-withdrawing group, which enhances resonance stabilization and increases acidity.
Final Answer: \[ \boxed{m\text{-chlorophenol}} \]