Question

In the presence of peroxide, HCl and HI do not give anit-Markownikoff's addition to alkenes because:

• A. one of the steps is endothermic in HCl and HI
• B. both HCl and HI are strong acids
• C. HCl is oxidizing and the HI is reducing
• D. all the steps are exothermic in HCl and HI

Answer 1

Answer: (A)

one of the steps is endothermic in HCl and HI

In the presence of organic peroxides, bromides will take part in radical based reactions. Fission of the peroxide O-O linkage will induce a Br radical which behaves differently to Bromide, by adding to the less substituted side of the alkene (anti - markovnikov). HI and HCl do not do this for energetic reasons.

The addition of Cl and I radicals to the alkene in an anti-markovnikov fashion is an endothermic reaction and therefore unfavourable. Without the presence of peroxide, all hydrogen halides will add according to the markovnikov rule.
Hence, option A is the correct answer.