MolSynapsequestion bank
MolSynapse / Question bank / Aldehydes, Ketones and Carboxylic Acids / Carboxylic acids: acidity, preparation, derivatives, HVZ reaction
JEE Advanced levelSingle correct optionDifficulty 3 of 3co204

Assertion (A): o-Nitrobenzoic acid (pKa 2.17) is a stronger acid than p-nitrobenzoic acid (pKa 3.44). Reason (R): The effect of the nitro group falls off with distance and is largest at the ortho position, and the ortho substituent also twists the carboxyl group out of the ring plane (ortho effect); both factors stabilise the carboxylate more in the ortho isomer. Choose the correct option.

  1. ABoth A and R are true and R is the correct explanation of A
  2. BBoth A and R are true but R is not the correct explanation of A
  3. CA is true but R is false
  4. DA is false but R is true

Answer: A

A is true because 2.17 < 3.44. R is true: the inductive withdrawal is strongest at the nearby ortho position and the ortho effect (steric inhibition of resonance of the carboxyl group with the ring) further increases acidity. These are the accepted reasons for the higher acidity of the ortho isomer, so R explains A.
Practice Aldehydes, Ketones and Carboxylic Acids More on Carboxylic acids: acidity, preparation, derivatives, HVZ reaction
Previous questionNext question

More questions on Carboxylic acids: acidity, preparation, derivatives, HVZ reaction