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JEE Advanced levelSingle correct optionDifficulty 3 of 3o2204

3,3-Dimethylbut-1-ene is treated with (i) in the presence of peroxide and (ii) in the presence of peroxide. The major products are

  1. A(i) 1-iodo-3,3-dimethylbutane; (ii) 1-bromo-3,3-dimethylbutane
  2. B(i) 1-iodo-3,3-dimethylbutane; (ii) 2-bromo-2,3-dimethylbutane
  3. C(i) 2-iodo-2,3-dimethylbutane; (ii) 1-bromo-3,3-dimethylbutane
  4. D(i) 2-iodo-2,3-dimethylbutane; (ii) 2-bromo-2,3-dimethylbutane

Answer: C

The peroxide effect works only for HBr, where both radical chain steps are favourable. With HI the addition is too endothermic, so the ionic path with a methyl shift gives 2-iodo-2,3-dimethylbutane. With HBr the radical path gives the anti-Markovnikov, unrearranged bromide.
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