Alkene Addition Reaction

Correct Answer: B

This is the Anti-Markovnikov alkene addition by the combination of HBr and organic peroxides (ROOR). Normally, HBr addition to alkenes occurs via a carbocation pathway and leads to the Markovnikov addition product. However, when you throw in peroxides, the mechanism of the reaction changes to a free-radical process. As a result, the bromine gets added to the less substituted carbon and the hydrogen gets added to the more substituted carbon of the original alkene (Anti-Markovnikov addition). There are no carbocation rearrangements in a free-radical process. Finally, a lot of people thought the answer was A. Count yer carbons!