Question

Assertion (A) : Phenol is more acidic than 4-methylphenol. Reason (R) : The presence of an electron releasing group in phenol makes it more acidic.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

Electron withdrawing groups increase acidity of phenols, while electron donating groups such as CH$_3$, OCH$_3$ and NH$_2$ decrease acidity.

Answer 1

The Correct Option is C

Concept: Acidity depends upon the stability of the conjugate base formed after loss of a proton. For phenol: \[ C_6H_5OH \] loss of proton gives phenoxide ion: \[ C_6H_5O^- \] The more stable the phenoxide ion, the greater is the acidity of phenol. Electron withdrawing groups increase acidity, whereas electron donating groups decrease acidity.

Step 1: Compare phenol and 4-methylphenol. Phenol: \[ C_6H_5OH \] 4-Methylphenol (p-cresol): \[ CH_3-C_6H_4-OH \] The methyl group is an electron donating group.

Step 2: Effect of methyl group. The methyl group exerts a positive inductive effect (+I effect). This effect pushes electron density towards the aromatic ring. Consequently, the phenoxide ion becomes less stable because additional electron density is added to an already negatively charged species.

Step 3: Compare acidity. Since phenoxide ion is more stable than p-methylphenoxide ion: \[ \text{Phenol} \gt \text{4-Methylphenol} \] in acidity. Therefore, the Assertion is true.

Step 4: Analyze the Reason. The Reason states that the presence of an electron releasing group in phenol makes it more acidic. This statement is incorrect. Electron releasing groups actually decrease acidity because they destabilize the conjugate base. Hence the Reason is false.

Final Conclusion: Assertion is true but Reason is false. \[ \boxed{\text{Option (C)}} \]