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 order 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) group at any position shows electron withdrawing effect thus acid strength is increased. But o-nitro benzoate ion is stabilised by intramolecular H-bonding, hence its acid strength is maximum, The effect is more at para position than meta. Thus, acid strength (II) > (III) > (IV) > (I)