Question

Consider the acidity of the carboxylic acids:

(1) PhCOOH

(2) o-NO₂C₆H₄COOH

(3) p-NO₂C₆H₄COOH

(4) m-NO₂C₆H₄COOH

Options

• 2 > 3 > 4 > 1

• 2 > 4 > 3 > 1

• 2 > 4 > 1 > 3

• 1 > 2 > 3 > 4

Answer 1

2 > 3 > 4 > 1

Explanation:

The -R and -I effects of the nitro group are more pronounced at the ortho and para positions than at the meta position. This makes ortho and para-nitrobenzoic acids stronger than the meta isomer. Ortho-nitrobenzoic acid is more acidic than para-nitrobenzoic acid. This is due to the ortho effect, which is caused by steric hindrance.