Chemistry Alcohols & Phenols MDCAT 2017
PMDC Verified Question 80 of 95
The acidity of phenol is due to its ____:
A
Nature of Benzene
B
Nature of phenoxide
C
Double bond in benzene ring
D
Hydroxyl group
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Nature of phenoxide
Concept:

Acidity is thermodynamically driven by the stability of the anion formed after the proton is lost.

Formula:

$$ \text{C}_6\text{H}_5\text{OH} \rightleftharpoons \text{C}_6\text{H}_5\text{O}^- + \text{H}^+ $$

Solution:

  • Phenol acts as an acid because it yields a proton to form a phenoxide ion.


  • The nature of the phenoxide ion—specifically its ability to stabilize the resulting negative charge through resonance—is the direct cause of phenol's enhanced acidity compared to aliphatic alcohols.


Why other options are incorrect:

The hydroxyl group alone (Option D) doesn't guarantee strong acidity (e.g., ethanol). The nature of benzene (Option A) or its double bonds (Option C) are incomplete explanations; the critical factor is the electronic behavior of the resulting conjugate base (phenoxide).

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