Question

In presence of peroxide, hydrogen chloride and hydrogen iodide do not give anti-Markovnikov's addition to alkenes because 

(a) both are highly ionic 

(b) one is oxidising and the other is reducing 

(c) one of the steps is endothermic in the both cases 

(d) all the steps are exothermic in the both the cases 

Answer 1

(c) one of the steps is endothermic in the both cases

In the presence of peroxide, HCl and HI reaact with alkenes as follows.

1^st step:

For HCl step I (b) is endothermic and step II is exothermic. While for HI step I

(b) is exothermic and step II is endothermic. 

Hence, in each case, one of the steps is exothermic. 

Due to this reason HCl and HI do not give anti -Markownikoff's addition to alkenes.

Answer 2

(c) one of the steps is endothermic in the both cases