Halogenation

Halogenation is a chemical reaction that replaces a hydrogen atom with a halogen atom. More specific descriptions exist that specify the type of halogen: fluorination, chlorination, bromination, and iodination.

In a Markovnikov addition reaction, a halogen like bromine is reacted with an alkene which causes the π-bond to break forming an haloalkane. This makes the hydrocarbon more reactive and bromine as it turns out, is a good leaving group in further chemical reactions such as nucleophilic aliphatic substitution reactions and elimination reactions

Several types of halogenation exist, including:

Bromination

bromination reaction mechanism

The reaction mechanism for an alkene bromination can be described as follows. The bromine - bromine covalent bond attracts the attention of the π-bonding electrons, the π-bonds being electron dense and Bromine being very electronegative. This leads to a weakening and eventual break where heat, plays a crucial role in driving the break forward of the π-bond. Once the π-bond has been broken, its electrons are transfered to Br₂, causing the Br-Br bond to be severed when the bonding electrons are transfered to the other bromine. At this stage there is the positively charged intermediate and the loose bromine ion (Br^-). The bonding of Bromine is special in this intermediate, due to its relatively large size compared to carbon, the bromide ion is capable to latching onto both carbons which once formed the π-bond, making a three-membered ring. Coming from the opposite direction as the Br₂, the Br^- loosens one of the C-Br Bonds, leaving the final brominated product, a brominated alkane.

Bromination

See also