Question

Given are cyclohexanol (I), acetic acid (II), 2,4,6-trinitrophenol (III) and phenol (IV). In these the order of decreasing acidic character will be:

• A. III > II > IV > I
• B. II > III > I > IV
• C. II > III > IV > I
• D. II > IV > II > I

Answer 1

The correct option is A III > II > IV > I

Since, phenols and carboxylic acids are more acidic than aliphatic alcohols, we find that cyclohexanol (I) is least acidic. Out of the two given phenols, III is more acidic than IV. This is because of the presence of three highly electron withdrawing $–N{O}_2$ groups on the benzene ring which makes the $O-H$ bond extremely polarized. This facilitates the release of $H$ as $H^{+}$. Thus, III > IV.
In acetic acid, the electron withdrawing $-C=O$ in the $-COOH$ group polarises the $O-H$ bond and increases the acidic strength. Acetic acid is therefore more acidic than phenol or cyclohexanol. The order of acidic character is III > II > IV > I.