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 are more acidic than alcohols because the phenoxide ion formed after proton dissociation (\( \text{H}^+ \)) is stabilized by resonance. This resonance spreads the negative charge on the oxygen, increasing acidity. Electron-withdrawing groups, like -Cl, further boost phenol acidity by stabilizing the negative charge on the oxygen atom.
Step 1: Comparative structural analysis.
Benzyl alcohol: Exhibits lower acidity; the hydroxyl group is bonded to a saturated carbon, precluding resonance stabilization.
Cyclohexanol: Comparable to benzyl alcohol; it lacks resonance stabilization and thus has reduced acidity.
Phenol: Demonstrates higher acidity owing to resonance stabilization of the phenoxide ion.
m-Chlorophenol: Possesses the highest acidity; the -Cl substituent acts as an electron-withdrawing group, intensifying resonance stabilization and elevating acidity.
Final Answer:\[\boxed{m\text{-chlorophenol}}\]