The mechanism (Radical Addition to symmetrical alkenes)
المؤلف:
University of Missouri System
المصدر:
Organic Chemistry ii
الجزء والصفحة:
.................
4-10-2020
1690
The mechanism (Radical Addition to symmetrical alkenes)
Hydrogen halides (hydrogen chloride, hydrogen bromide and the rest) usually react with alkenes using an electrophilic addition mechanism. However, in the presence of organic peroxides, hydrogen bromide adds by a different mechanism.
With the organic peroxides present you get a free radical chain reaction.
Chain initiation
The chain is initiated by free radicals produced by an oxygen-oxygen bond in the organic peroxide breaking.
These free radicals extract a hydrogen atom from a hydrogen bromide molecule to produce bromine radicals.
Chain propagation
A bromine radical joins to the ethene using one of the electrons in the pi bond. That creates a new radical with the single electron on the other carbon atom.
That radical reacts with another HBr molecule to produce bromoethane and another bromine radical to continue the process.
etc
Chain termination
Eventually two free radicals hit each other and produce a molecule of some sort. The process stops here because no new free radicals are formed.
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