Addition of $\mathrm{HBr}$ to propene in presence of a peroxide takes place contrary to Markovnikov rule. This can be explained by the mechanism involving

Addition of $\mathrm{HBr}$ to propene in presence of a peroxide takes place contrary to Markonikov rule. This reaction is known as peroxide or kharash effect or addition reaction anti to Markonikov rule. Peroxide effect proceeds via free radical chain mechanism as given below:
Benzoyl peroxide.