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JEE Main levelSingle correct optionDifficulty 2 of 3g1269

2,6-Dimethyl substitution makes the acid shown stronger than benzoic acid. The best explanation is

  1. Athe methyl groups withdraw electrons by the -I effect
  2. Bthe COOH group is twisted out of the plane of the ring, so the ring cannot donate to it by resonance
  3. Cthe methyl groups stabilise the undissociated acid by hyperconjugation
  4. Dthe ring becomes antiaromatic

Answer: B

The acid shown is 2,6-dimethylbenzoic acid. The two ortho methyl groups twist the COOH group out of the ring plane, so the ring cannot donate electrons to the carboxyl group by resonance. This steric inhibition of resonance (the ortho effect) makes the acid stronger.
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