Free radical addition

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Free radical addition is an addition reaction in organic chemistry.

The basic steps with examples are:

Initiation: H-O-O-H -> H-O* H-O* + Br-Br -> H-O-Br Br*.
Propagation: Br* + H2CCH2 -> H-Br + *CHCH2.
Termination: H3C* + Br-Br -> Br* + BrCH3.

Free radical addition depends on one of the reagents having a (relatively) weak bond. Having a weak bond means that (said reagent) will easily break apart to form radicals (often with heat or light), whereas having a strong bond will probably force any reactions to use a different mechanism.

To illustrate, consider the alkoxy radical-catalyzed, anti-Markovnikov reaction of hydrogen bromide to an alkene. In this reaction, a small amount of organic peroxide (R-O-O-R') is needed to abstract the acidic proton from HBr and generate the Br.- radical, but it is assumed that there is one molar equivalent of alkene to acid in order to balance the equation.

Initiation:

Image:Rxn step 1.jpg Image:Rxn 1 step 2.jpg

Propagation:

Image:TheDaoOf42 rxn 1 step 3.jpg

Note that the radical will be on the more substituted carbon.

Image:TheDaoOf42 rxn 1 step 4.jpg

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