Question

What is the correct order of acidity of compounds I, II and III?
i. 4-Nitrobenzoic acid
ii. 4-Methoxy Benzoic acid
iii. Benzoic acid

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

Answer 1

Answer: (A)

I>III>II

Answer 2

The correct answer is option (A): I>III>II
The acidity can be determined by the stability of the conjugate base formed after losing a proton. More stable the conjugate more stronger the acid. I: 4-Nitrobenzoic acid: it has a strong electron-withdrawing group. The negative charge on the base is stabilized by the electron-withdrawing effect of the nitro group. II 4-Methoxybenzoic acid: The methoxy group is attached to the beneze ring. The Methoxy group is electron donating but is not as effective as the nitro group. III Benzoic acid: It has no substituent group Therefore, the order of acidity will be I>III>II