Q36 / 160 · AP EAMCET 2018 (23 Apr Shift 2) · Chemistry

Identify the correct set from the following Compound $p K_a \quad$ Compound $p K_a$

  • A
    $m$-nitrophenol 10.2
  • B
    o-nitrophenol 10.2
  • C
    $m$-nitrophenol 7.2
  • Correct answer
    D
    o-nitrophenol 7.2

Solution

In $o$-nitrophenol there is intramolecular $\mathrm{H}$-bonding, since $-\mathrm{NO}_2$ group is very close to - $\mathrm{OH}$ group. Thus, proton can not be easily released from $o$-nitrophenol as compared to para and meta. Thus, $\mathrm{p} K_a$ is least.

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

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