Q.1 (viii) The highest acidic compound among the following is _____.
A. [Structure: benzoic acid with OH at the meta position (m-hydroxybenzoic acid)]
B. [Structure: benzoic acid with NH2 at the ortho position (o-aminobenzoic acid)]
C. [Structure: benzoic acid]
D. [Structure: benzoic acid with OCH3 at the para position (p-methoxybenzoic acid)]
Best answer
Answer: A. [Structure: benzoic acid with OH at the meta position (m-hydroxybenzoic acid)]
Answer: (a) m-hydroxybenzoic acid
Electron-withdrawing effects stabilise the carboxylate ion and increase acidity; electron-donating (+R) effects decrease it. At the meta position the −OH group cannot donate electrons by resonance to the −COO− carbon, so only its −I effect operates and m-hydroxybenzoic acid is slightly stronger than benzoic acid. The p-OCH3 group donates electrons by +R effect, and the o-NH2 group is strongly electron-donating and basic, so both are weaker acids than benzoic acid. Order: (a) > (c) > (d) > (b).
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