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JEE Advanced levelSingle correct optionDifficulty 3 of 3o1262

Assertion (A): Lithium aluminium hydride reduces the amide shown to an amine, whereas it reduces esters to alcohols. Reason (R): In the tetrahedral intermediate formed from the amide, the oxygen (as an aluminate) is lost rather than the poor leaving group , giving an iminium ion that is reduced further. Choose the correct option.

  1. ABoth A and R are true and R is the correct explanation of A
  2. BBoth A and R are true but R is not the correct explanation of A
  3. CA is true but R is false
  4. DA is false but R is true

Answer: A

N,N-Dimethylbenzamide is reduced to benzyldimethylamine. In the tetrahedral intermediate the amide anion is a very poor leaving group, so the O-Al bond breaks and an iminium ion forms and takes a second hydride. In an ester the alkoxide is a viable leaving group, so an aldehyde forms and is reduced to a primary alcohol. Both statements are true and R explains A.
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