Question

Arrange the following in the correct order of their acidic strength: I. \( \text{C}_6 \text{H}_4 (\text{OH}) \) (I) II. \( \text{C}_6 \text{H}_5 (\text{OH}) \) (II) III. \( \text{C}_6 \text{H}_4 (\text{NO}_2)(\text{OH}) \) (III) IV. \( \text{C}_6 \text{H}_4 (\text{NO}_2)(\text{OH}) \) (IV)

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

Hint:

Electron-withdrawing groups like \( \text{NO}_2 \) increase acidity, while electron-donating groups like \( \text{OH} \) decrease acidity.

Answer 1

The Correct Option is B

Step 1: The strength of the acid is determined by the ability of the molecule to donate a proton (H\(^+\)). The electron-withdrawing groups, such as \( \text{NO}_2 \), enhance the acidic strength by stabilizing the conjugate base. The electron-donating groups, such as \( \text{OH} \), make the molecule less acidic.
Step 2: Arranging based on acidic strength: - Option (IV) \( \text{C}_6 \text{H}_4 (\text{NO}_2)(\text{OH}) \): The \( \text{NO}_2 \) group, being highly electron-withdrawing, increases the acidity. - Option (III) \( \text{C}_6 \text{H}_4 (\text{NO}_2)(\text{OH}) \): The \( \text{NO}_2 \) group is still electron-withdrawing, but slightly less than in option IV. - Option (I) \( \text{C}_6 \text{H}_5 (\text{OH}) \): The \( \text{OH} \) group is electron-donating, which decreases the acidity. - Option (II) \( \text{C}_6 \text{H}_4 (\text{OH}) \): This is the least acidic because of the electron-donating effect of \( \text{OH} \). Thus, the order of acidic strength is IV > III > I > II.