Halogenation

Halogenation is a chemical reaction that replaces a hydrogen atom with a halogen atom. More specific words exist that specify which halogen: fluorination, chlorination, bromination, and iodination.

In a Markovnikov additon reaction (see Bromination below), bromine is added to an alkene, this causes the π-bond to break forming an alkane. This makes the hydrocarbon more reactive, bromine as it turns out, is a good leaving group in further chemical reactions such as S_n1, S_n2, E1 and E2

Several types of halogenation exist, including:

• free radical halogenation
• ketone halogenation
• Electrophilic halogenation

Bromination

    File:Bromination.png

The Br-Br bond attracts the attention of the π-bonding electrons (π-bonds being e^- dense and Br being very electronegative), this leads to a weakening and eventual break (heat, plays a crucial role in driving the break forward) of the π-bond. Once the π-bond has been broken, it's 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 positivly charged intermidiate and the loose bromine ion (Br^-). Bromine is somewhat special, due it's realativly large size (compare 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.

See also

• Halogenoalkanes (Alkyl halides)
• Halogenoarenes (Aryl halides)
• Electrophilic substitution