In the presence of peroxide, HCl and HI do not give anti-Markovnikov’s addition to alkenes because

(1) All the steps are exothermic in HCl and HI

(2) One of the steps is endothermic in HCl and HI

(3) HCl is oxidizing and the HI is reducing

(4) Both HCl and HI are strong acids

Answer ::

Bromides will take part in radical based reactions in the presence of organic peroxides. Fission of the peroxide O-O linkage causes a Br radical which behaves differently to Bromide, by adding to the less substituted side of the alkene(anti – markovnikov). HI and HCl does 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. Hence it is unfavourable. All hydrogen halides will add according to the markovnikov rule, without the presence of peroxide,