When Br2 is added to 1-methylcyclopentane, bromination occurs primarily at the carbon with the methyl substituent due to its higher reactivity. The expected product is bromocyclopentane, specifically 1-bromo-1-methylcyclopentane, rather than the proposed structures. The reaction mechanism involves radical formation, which is influenced by the conditions under which the reaction is conducted, such as mixing versus burning. Understanding the reactive groups and the mechanism is crucial for predicting the correct product. Overall, the formation of bromocyclopentane from Br2 and 1-methylcyclopentane highlights the importance of reaction conditions and substitution patterns.