The acid shown has $p K_{a} = 4.37$ (benzoic acid 4.20; 4-nitrobenzoic acid 3.44; 4-methoxybenzoic acid 4.47). Which statements are correct?

AIt is a weaker acid than benzoic acid
BIt is a stronger acid than 4-methoxybenzoic acid
CIt is a stronger acid than 4-nitrobenzoic acid
DIts $K_{a}$ is between 0.6 and 0.7 times that of benzoic acid

Answer: A, B, D

The drawn compound is 4-methylbenzoic (p-toluic) acid. The +I/hyperconjugation of CH3 destabilises the carboxylate, so pKa 4.37 > 4.20 (weaker than benzoic) but < 4.47 (stronger than the methoxy acid) and > 3.44 (weaker than nitro). Ka ratio

= 1 0^{(4.20 - 4.37)} = 0.676

, which lies between 0.6 and 0.7.

Practice Aldehydes, Ketones and Carboxylic Acids More on Acidity order and derivative reactivity among drawn carboxylic acids

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The acid shown has pKa​=4.37 (benzoic acid 4.20; 4-nitrobenzoic acid 3.44; 4-methoxybenzoic acid 4.47). Which statements are correct?

Answer: A, B, D

More questions on Acidity order and derivative reactivity among drawn carboxylic acids

The acid shown has $p K_{a} = 4.37$ (benzoic acid 4.20; 4-nitrobenzoic acid 3.44; 4-methoxybenzoic acid 4.47). Which statements are correct?