Question

Why can an anti-markovnikov radical addition of haloalkane only happen in presence of hydrogen peroxide?

Answer 1

In a "normal" Markovnikov attrition of `"HBr"` to an alkene, the `"H"` adds to the carbon with more hydrogen atoms in order to form the more stable carbocation.

Explanation:

In the peroxide-catalyzed addition, the bromine radical adds to the carbon with more hydrogen atoms in order to form the more stable radical.

That means that the `"H"` must go on the carbon with fewer `"H"` atoms.