Q60 / 180 · KCET 2018 · Chemistry

What is the increasing order of acidic strength among the following?
(i) p-methoxy phenol
(ii) p-methyl phenol
(iii) p-nitro phenol

  • A
    \( \mathrm{ii} < \mathrm{iii} < \mathrm{i} \)
  • B
    \( \mathrm{iii} < \mathrm{ii} < \mathrm{i} \)
  • Correct answer
    C
    \( \mathrm{i} < \mathrm{ii} < \mathrm{iii} \)
  • D
    \( \mathrm{i} < \mathrm{iii} < \mathrm{i} \)

Solution

Presence of \( -\mathrm{NO}_{2} \) group increases the acidic character of phenol, because it is an electron withdrawing group, it
withdraws the electron towards itself thereby decreasing the \( e^{-} \)density on the conjugate base so formed and stabilizes
by resonance, whereas the electron releasing groups increases the \( e^{-} \)density on conjugate base and destabilizes it.
Therefore, the increasing order of acidic strength is : \( | < \| < ||| \).

Hence, the correct answer is option: 'C'.

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