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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o4272

The enantiomerically pure halide shown is treated with the reagents below. Select all correct statements.

  1. ASodium azide in DMF gives mainly (R)-2-azidobutane.
  2. BPotassium tert-butoxide in tert-butanol gives mainly alkenes.
  3. CSodium azide in DMF gives racemic 2-azidobutane because the reaction passes through a planar carbocation.
  4. DPotassium tert-butoxide gives (R)-2-tert-butoxybutane as the main product.

Answer: A, B

The compound is (S)-2-bromobutane. Azide is a good nucleophile and weak base in a polar aprotic solvent, so the secondary halide reacts by SN2 with inversion, giving (R)-2-azidobutane (N outranks the ethyl group as Br did); a carbocation is not involved, so the product is not racemic. The bulky tert-butoxide cannot attack carbon readily and acts as a base, giving mainly butenes rather than the ether.
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