JEE Advanced levelSingle correct optionDifficulty 3 of 3g2156
Which of the following statements about 2,6-dimethylbenzoic acid is correct?
AIts COOH group is twisted out of the plane of the ring, and it is a stronger acid than benzoic acid
BIts COOH group is coplanar with the ring, and it is a weaker acid than benzoic acid because of the +I effect of two methyl groups
CIt is a weaker acid than benzoic acid because the methyl groups donate electrons by hyperconjugation
DIts acidity is the same as that of benzoic acid because methyl groups are far from the COOH
Answer: A
Two ortho methyl groups crowd the carboxyl group and twist it out of the plane. This steric inhibition of resonance (the ortho effect) outweighs their small electron-releasing effect, giving a lower pKa (3.25) than benzoic acid (4.20).