Addition of HBr to propene yields 2-bromopropane, while in the presence of benzoyl peroxide, the same reaction yields 1-bromopropane. Explain and give mechanism.

Explanation

Addition of HBr to propene is an ionic electrophilic addition reaction in which the electrophile, i.e., `H^+` first adds to give a more stable `2^@` carbocation. In the 2nd second, the carbocation is rapidly attacked by the nucleophile `Br^-` ion to give 2-bromopropane

In presence of benzoyl peroxide , the reaction is still electrophilic but the electrophile here is a `oversetdot(Br)` free radical which is obtained by the action of benzoyl peroxide on HBr

In the first step, `oversetdot(Br)` radical adds to propene in such a way as to generate a more stable `2^@` radical . In the second step, the free radical thus obtained rapidly abstracts a hydrogen atom from HBr to give 1-bromopropane.

it is evident that although both reactions (i.e., in presence or absence of benzoyl peroxide ) are electrophilic addition but it is due to different order or sequence of addition of H and Br atoms which gives different products.