Eduprobe
Question:
In the presence of peroxide, HCl and HI do not give anti-Markownikoff's addition to alkenes because:
one of the steps is endothermic in HCl and HI
both HCl and HI are strong acids
all the steps are exothermic in HCl and HI
HCl is oxidizing and the HI is reducing
Solution:
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.