Why does Peroxide not shown by …

HCl and HI do not give anti-Markovnikov addition to alkenes because some of the steps in the chain reaction are endothermic.

Explanation:

Reaction with HBr

The mechanism for anti-Markovnikov addition of HBr is:

Step 1. Abstraction of H from HBr (highly exothermic).

HO⋅+H-Br→HOH+⋅Br

Step 2

 Addition of Br⋅ to the alkene (exothermic)

CH3CH=CH2+⋅Br→CH3⋅CH-CH2Br

Step 3. The carbon radical abstracts another H from HBr (exothermic)

CH3⋅CH-CH2Br+H-Br→CH3CH2-CH2Br+⋅Br

The reaction is favourable because all the steps are exothermic.

Reaction with HCl

The reaction with HCl is unfavourable because the H-Cl bond is much stronger than the H-Br bond.

Step 1 is endothermic, and the reaction becomes too slow to be useful.

Reaction with HI

Step 1 is favourable, because the H-I bond is relatively weak.

But Step 2, addition of I⋅ to the alkene, is unfavourable and endothermic because of the bulk of the iodine radical.