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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g3109

Which of the following statements about the Hofmann and Curtius rearrangements are correct?

  1. AThe amine formed in the Hofmann degradation has one carbon fewer than the amide.
  2. BThe migrating group moves from carbon to nitrogen with retention of configuration.
  3. CHeating an acyl azide gives an isocyanate with loss of .
  4. DHofmann degradation of benzamide gives benzylamine.

Answer: A, B, C

In both reactions an alkyl or aryl group migrates from the carbonyl carbon to the electron-poor nitrogen with retention, giving an isocyanate . The Curtius route does this by loss of from the acyl azide. Hydrolysis of the isocyanate loses , so the product has one carbon fewer. Benzamide therefore gives aniline, , not benzylamine.
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