Question

Which of the following aromatic acids has less acidic strength than benzoic acid?

• A. o - nitrobenzoic acid
• B. p - methoxy benzoic acid
• C. m - nitrobenzoic acid
• D. o - chloro benzoic acid

Hint:

Electron-donating groups, like -OCH\(_3\), decrease the acidity of aromatic acids, while electron-withdrawing groups, like -NO\(_2\), increase the acidity.

Answer 1

The Correct Option is B

Step 1: Understanding the effect of substituents.
The acidity of benzoic acid is influenced by substituents attached to the benzene ring. Electron-withdrawing groups (such as -NO\(_2\)) increase the acidity by stabilizing the negative charge on the conjugate base, while electron-donating groups (such as -OCH\(_3\)) decrease the acidity. Methoxy (-OCH\(_3\)) is an electron-donating group, so it decreases the acidity compared to benzoic acid.
Step 2: Analyzing the options.
(A) o - nitrobenzoic acid: Incorrect. Nitro (-NO\(_2\)) is an electron-withdrawing group and increases the acidity.
(B) p - methoxy benzoic acid: Correct. Methoxy (-OCH\(_3\)) is an electron-donating group, which decreases the acidity of the acid.
(C) m - nitrobenzoic acid: Incorrect. Similar to o-nitrobenzoic acid, this will have increased acidity due to the electron-withdrawing nitro group.
(D) o - chloro benzoic acid: Incorrect. Chlorine is also an electron-withdrawing group, and it increases the acidity compared to benzoic acid.
Step 3: Conclusion.
The correct answer is (B) p - methoxy benzoic acid, as it has less acidic strength than benzoic acid due to the electron-donating effect of the methoxy group.