What type of fission occurs when Br reacts with alkenes?

The reaction between bromine (Br2) and alkenes typically involves the formation of a bromonium ion intermediate, which indicates that the type of fission occurring is heterolytic fission. In this context, heterolytic fission refers to the breaking of a chemical bond where one atom retains both electrons from the bond, resulting in the generation of charged species. When bromine reacts with an alkene, the Br-Br bond breaks, and one bromine atom forms a bond with one of the carbon atoms of the alkene while the other bromine becomes a bromide ion (Br-).

This reaction proceeds through electrophilic addition, where the alkene acts as a nucleophile due to its electron-rich double bond, and bromine acts as an electrophile. The generation of the bromonium ion is a crucial step that stabilizes the reaction intermediate and leads to the formation of dibrominated products.

Understanding this mechanism is key for students as it highlights how bond cleavage can lead to the formation of charged species and the significance of reaction intermediates in organic chemistry.