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NEET levelSingle correct optionDifficulty 1 of 3g2011

Phenol is a stronger acid than ethanol because

  1. Athe phenoxide ion is stabilised by delocalisation of the negative charge into the benzene ring, while the ethoxide ion has no such resonance
  2. Bthe benzene ring is electron rich and donates electrons to oxygen in the phenoxide ion
  3. Cthe ethyl group withdraws electrons by -M effect from the oxygen of the ethoxide ion
  4. Dthe O-H bond in ethanol is stronger because ethanol cannot form hydrogen bonds

Answer: A

Loss of H+ from phenol gives a phenoxide ion whose charge is delocalised over the ortho and para carbons through resonance. Ethoxide has the charge localised on oxygen, further intensified by the +I effect of the ethyl group. The better stabilised conjugate base makes phenol (pKa 10.0) a stronger acid than ethanol (15.9).
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