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JEE Advanced levelSingle correct optionDifficulty 3 of 3g1050

Acetamide, , is protonated on oxygen rather than on nitrogen because

  1. Athe C=O bond is non-polar
  2. Bthe O-protonated cation is stabilised by delocalisation of the nitrogen lone pair, while N-protonation would take that lone pair out of conjugation
  3. Cthe nitrogen lone pair is localised and unavailable because of the +I effect of the methyl group
  4. Doxygen is less electronegative than nitrogen

Answer: B

The nitrogen lone pair of an amide is delocalised toward the carbonyl carbon. Protonation on O gives a cation whose positive charge is shared between N and C and O, as in . Protonation on N uses that lone pair and gives an ion with no such delocalisation.
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