A halogen addition reaction involves adding halogen atoms such as bromine (Br₂) to an alkene.
This process is generally followed by a series of steps that entail the interaction of the halogen molecules with the pi bonds in the alkene.
This reaction usually proceeds through an anti-addition mechanism, meaning the two halogen atoms add to opposite sides (anti) of the double bond.
The steps are generally:
- A halogen molecule like Br₂ approaches the double bond.
- The electron-rich double bond attacks the bromine molecule, leading to the formation of a cyclic bromonium ion.
- Then, the bromonium ion opens as a bromide ion attacks from the opposite side, resulting in anti-addition.
This leads to the formation of vicinal dihalides, where the added halogens are on adjacent carbons.