question_answer

Consider the acidity of the carboxylic acids  (i)\[PhCOOH\] (ii)\[o-N{{O}_{2}}{{C}_{6}}{{H}_{4}}COOH\] (iii)\[p-N{{O}_{2}}{{C}_{6}}{{H}_{4}}COOH\] (iv)\[m-N{{O}_{2}}{{C}_{6}}{{H}_{4}}COOH\] Which of the following orders is correct?

A)  (i) > (ii) > (iii) > (iv)

B)  (ii) > (iv) > (iii) > (i)

C)   (ii) > (iv) > (i) > (iii)

D)   (ii) > (iii) > (iv) > (i)

Correct Answer: D

Solution :

(i)                           (ii) (iii)                         (iv) \[-N{{O}_{2}}\]group at any position shows electron withdrawing effect, thus acid strength is increased. But \[o-\]nitro benzoate ion is stabilised by intra molecular \[H-\]bonding like forces, hence its acid strength is maximum. Thus, the order of acid strength is (ii) > (iii) > (iv) > (i).