Question

Which of the following is the strongest acid?

• A. \( p\)-Cl – \( C_6H_4\text{COOH} \)
• B. \( p\)-OH – \( C_6H_4\text{COOH} \)
• C. \( C_6H_5\text{COOH} \)
• D. \( p\)-NO\(_2\) – \( C_6H_4\text{COOH} \)

Hint:

The greater the electron-withdrawing effect, the stronger the acid due to better conjugate base stabilization.

Answer 1

The Correct Option is D

The acidity of benzoic acid derivatives depends on the electron-withdrawing or electron-donating nature of the substituent at the para position: - Electron-withdrawing groups (like \( NO_2 \)) increase acidity by stabilizing the conjugate base through delocalization. - Electron-donating groups (like \( OH \) or \( CH_3 \)) decrease acidity by increasing electron density on the carboxyl group. Since \( p\)-NO\(_2\) is a strong electron-withdrawing group, it stabilizes the conjugate base, making benzoic acid more acidic.