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JEE Main 2023 · Chemistry · General Organic Chemistry and Isomerism · easy

The correct order of acidic strength of the following phenols is: (I) phenol, (II) p-nitrophenol, (III) m-nitrophenol, (IV) p-methoxyphenol

Single correct option

The correct order of acidic strength of the following phenols is: (I) phenol, (II) pp-nitrophenol, (III) mm-nitrophenol, (IV) pp-methoxyphenol
  1. A. II > III > I > IV
  2. B. III > II > I > IV
  3. C. II > I > III > IV
  4. D. I > II > III > IV
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Answer: (A) II > III > I > IV

Electron-withdrawing groups stabilise the phenoxide. The pp-NO2\mathrm{NO_2} group exerts both −R-R and −I-I effects (pKa≈7.1K_a\approx7.1), the mm-NO2\mathrm{NO_2} group only −I-I (pKa≈8.4K_a\approx8.4), phenol is pKa≈10K_a\approx10, and the pp-OCH3\mathrm{OCH_3} group is electron-donating by +R+R (pKa≈10.2K_a\approx10.2), destabilising the anion. Order: II > III > I > IV.
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