In the presence of peroxides, hydrohalogenation of asymmetrical alkenes proceeds with what regiochemistry?

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Regioselectivity in peroxide-initiated hydrohalogenation of alkenes is what's being tested. The presence of peroxides starts a radical chain that changes how HBr adds across the double bond. Initiation generates radicals from the peroxide, which then convert HBr into Br• radicals. The bromine radical preferentially adds to the less substituted carbon of the double bond, creating a radical on the more substituted carbon. That carbon-centered radical then abstracts a hydrogen atom from another molecule of HBr, forming the anti-Markovnikov alkyl bromide and regenerating Br• to keep the chain going. So the bromine ends up on the less substituted carbon, giving the anti-Markovnikov product (for example, propene gives 1-bromopropane with peroxide). Without peroxides, the reaction would follow the ionic, Markovnikov pathway, putting Br on the more substituted carbon. The option about no reaction isn’t correct because the radical mechanism drives the process under these conditions, and the idea of radical addition at a conjugated site isn’t the general pattern for simple alkenes under these conditions.