Q37 / 160 · AP EAMCET 2023 (15 May Shift 2) · Chemistry

Which of the following has more $\mathrm{pK}_{\mathrm{a}}$ value?

  • A
    2-Nitrophenol
  • Correct answer
    B
    3-Nitrophenol
  • C
    4-Nitrophenol
  • D
    2, 4-Dinitrophenol

Solution

Greater $\mathrm{pK}_{\mathrm{a}}$ value means smaller $\mathrm{K}_{\mathrm{a}}$ or weaker acid. Due to the presence of an electron-withdrawing $-\mathrm{NO}_2$ group at the meta position, 3- nitrophenol is the weakest acid among the given options. The effect of $-\mathrm{NO}_2$ is nullified at the meta position.

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

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