Question

Consider the acidity of the carboxylic acids (i) PhCOOH (ii) $o-NO_2C_6H_4COOH$ (iii) $p-NO_2C_6H_4COOH$ (iv) $m-NO_2C_6H_4COOH$ 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)

Answer 1

Answer: (D)

(ii) > (iii) > (iv) > (i)

Answer 2

$-NO_2$ group at any position shows electron withdrawing effect, thus acid strength is increased, but o-nitro benzoate ion is stabilised by intramoiecuiar H-bonding like forces, hence
its acid strength is maximum.
Thus, the order of acid strength is (ii) > (iii) > (iv) > (i).