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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o2109

Which of the following statements regarding the addition of HX to alkenes under radical conditions are correct?

  1. AFor HCl, the H-abstraction step by the carbon radical is endothermic
  2. BFor HI, the addition of to the double bond is unfavourable (endothermic, reversible)
  3. CFor HBr, both propagation steps are favourable
  4. DHF shows a pronounced peroxide effect

Answer: A, B, C

The H-Cl bond is too strong for the chain-transfer step to be exothermic, and is too stable and unreactive to add readily to alkenes, so only HBr sustains the radical chain. HF has an extremely strong H-F bond and shows no peroxide effect.
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