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JEE Advanced levelSingle correct optionDifficulty 3 of 3o2104

2-Methylbut-2-ene is treated with HBr in the presence of a peroxide. The major product and its optical behaviour are

  1. A2-bromo-3-methylbutane, formed as a single enantiomer
  2. B2-bromo-3-methylbutane, formed as an optically inactive racemic mixture
  3. C2-bromo-2-methylbutane, optically inactive because it is achiral
  4. D2-bromo-3-methylbutane, formed as a meso compound

Answer: B

adds to C-3, the carbon bearing one H, to give the tertiary radical . H abstraction from HBr takes place from either face, giving , which has one stereocentre and forms as equal amounts of both enantiomers (racemic, optically inactive). A meso form is not possible with one stereocentre.
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