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JEE Advanced levelSingle correct optionDifficulty 3 of 3hc071

2-Bromo-2,3-dimethylbutane is heated separately with (X) alcoholic KOH and (Y) potassium tert-butoxide in tert-butanol. Taking Saytzeff elimination with the small base and Hofmann elimination with the bulky base, the major alkenes from X and Y respectively are

  1. A2,3-dimethylbut-1-ene and 2,3-dimethylbut-2-ene
  2. B3,3-dimethylbut-1-ene and 2,3-dimethylbut-2-ene
  3. C2,3-dimethylbut-2-ene and 2,3-dimethylbut-2-ene
  4. D2,3-dimethylbut-2-ene and 2,3-dimethylbut-1-ene

Answer: D

With alcoholic KOH the more substituted tetrasubstituted alkene 2,3-dimethylbut-2-ene is the major product (Saytzeff). The bulky tert-butoxide removes the more accessible hydrogen from a methyl group, giving the less substituted 2,3-dimethylbut-1-ene (Hofmann). 3,3-Dimethylbut-1-ene would need a skeletal rearrangement and is not formed by E2.
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