Q76 / 200 · NEET 2005 · Chemistry

Which one of the following compounds is most acidic?

  • A
    Figure
  • B
    Figure
  • Correct answer
    C
    Figure
  • D
    Figure

Solution

Phenols are more acidic than alcohols, due to the stabilization of phenoxide ion via resonance. Ortho nitrophenol is most acidic of all because $-\mathrm{NO}_2$ is a electron withdrawing group. Thus, $\mathrm{NO}_2$ stabilise of negative charge on the oxygen of phenoxide ion. On the other hand, $\mathrm{CH}_3$ group is a electron donating group. Thus, acidic strength of phenol is decreased in cresol due to destabilisation of phenoxide ion. Thus, correct order is: Figure
Caution $\Rightarrow$ Phenoxide ion is stabilized due to following resonating structures:Figure

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

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