Final answer:
The major product of the reaction between an alkene and HBr with ROOR is the anti-Markovnikov addition product, while the minor product is the Markovnikov addition product. The reaction is regioselective, forming predominantly one constitutional isomer over another.
Step-by-step explanation:
The question is about a chemical reaction between an alkene and HBr in the presence of ROOR, which indicates that the reaction is likely to proceed via a radical mechanism. In such reactions, anti-Markovnikov addition occurs, leading to the formation of the major product where the Br atom attaches to the less substituted carbon atom. In the presence of ROOR, a peroxide, the reaction follows a radical pathway resulting in the anti-Markovnikov product. Hence, among the options provided (I, II, III, IV), the major product would be where the Br is attached to the less substituted carbon which is typically represented as Product I. The minor product would follow the Markovnikov rule where the Br attaches to the more substituted carbon typically represented as Product II. However, the minor product is usually formed in significantly lower amounts compared to the major product.
Chemical reactions like this one are regioselective because they yield predominantly one constitutional isomer over another. The radical initiator (ROOR) shifts the reaction pathway from the typical Markovnikov addition to an anti-Markovnikov addition, leading to the formation of a different major product than would be expected without the initiator.