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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g2247

The compound shown is an amide. Select ALL the correct statements about its protonation.

  1. AIt is a much weaker base than ethylamine.
  2. BProtonation occurs preferentially on oxygen.
  3. CProtonation on nitrogen gives the resonance-stabilised cation.
  4. DThe conjugate acid is stabilised by resonance with charge shared by N and O.

Answer: A, B, D

Acetamide protonates on oxygen (pKaH about -0.5), giving a cation stabilised by resonance (O-H and C=N+H2 forms), so the first two statements hold; the amide is about eleven pKa units weaker as a base than ethylamine (10.7). Protonation on nitrogen would leave the cation without this resonance, since the nitrogen lone pair is already used in conjugation.
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