Question

Which one of the following is strongly acidic?

• A. Phenol
• B. o-cresol
• C. p-Nitrophenol
• D. p-cresol

Answer 1

Answer: (C)

The acidity of phenols is due to the greater resonance stabilization of the phenoxide ion relative to phenol. Therefore, electron withdrawing groups (EWG) like $-N{O}_2$ which stabilize the phenoxide ion more by dispersing the negative charge will tend to increase the acidity of phenols.



On the other hand, electron donating groups (EDG) like-alkyl group destabilize the phenoxide ion by intensifying the negative charge relative to phenol tend to decrease the acidic strength of phenols.



As methyl group has $+l$ effect and it is stronger at o-position than at $p$ -position, $(+1$ effect decreases with distance $)o$ -cresol is a weaker acid than p-cresol.

Thus, the order of acidic strength.

$p$ - nitrophenol $>$ phenol $>p$ - cresol $>$ o-cresol