Question

Consider the acidity of the carboxylic acids:
(i) PhCOOH
(ii) o - NO₂C₆H₄COOH
(iii) p - NO₂C₆H₄COOH
(iv) m - NO₂C₆H₄COOH
Which of the following order is correct?
(a) i > ii > iii > iv (b) ii > iv > iii > i
(c) ii > iv > i > iii (d) ii > iii > iv > i.

Answer 1

Electron withdrawing group increases the acidity of benzoic acid, o - isomer will have higher acidity then corresponding m and p isomer due to ortho - effect. As M group (i.e. NO₂ ) at p -position have more pronounced electron withdrawing effect than as 

– NO₂ group at m - position (–I effect) 

Therefore,  Correct order of acidity is ii > iii > iv > i.