Four hydroxybenzoic and related acids are shown beside the options (the drawn compound is p-hydroxybenzoic acid, for reference). Which structure is the strongest acid?

AStructure A
BStructure B
CStructure C
DStructure D

Answer: C

2,6-Dihydroxybenzoic acid has pKa about 1.3: two ortho OH groups twist/crowd the carboxyl group (ortho effect) and each hydrogen-bonds to the carboxylate. Salicylic acid is 2.97, o-anisic acid 4.09 (crowding without chelation) and benzoic acid 4.20.

Practice General Organic Chemistry II: Acids and Bases More on Acidity order among drawn acids and phenols

Previous questionNext question

More questions on Acidity order among drawn acids and phenols

Four dicarboxylic acids are shown beside the options (the drawn compound is glutaric acid, for reference). Which structure has the lowest pK... JEE Main level
The compound shown is an unsaturated diacid. Compared with its geometric isomer, its pKa1 and pKa2 are respectively JEE Main level
The compound shown is a nitrophenol. Select ALL the correct statements about it. JEE Main level
Four chlorinated acids are shown beside the options (the drawn compound is propanoic acid, for reference). Which structure is the strongest ... JEE Main level
Four benzoic acids are shown beside the options (the drawn compound is benzoic acid, pKa 4.20). Select ALL the structures that are stronger ... JEE Advanced level
Four phenols are shown beside the options (the drawn compound is phenol, pKa 10.0). Which structure is the strongest acid? JEE Advanced level