20.6 : 自由基形成：加成

On the addition of a radical across the spin-paired π bond, it generates a new radical.

For instance, the bromine radical interacts with an alkene to produce a radical at a carbon center.

The mechanism of the reaction is based on spin conservation, similar to conservation of charge in a chemical reaction. So, a reactant with an unpaired electron forms a product with an unpaired electron.

The simplest radical addition reaction is the reduction process, where an electron is added to a spin-paired molecule.

One example is Birch reduction, where metals in liquid ammonia generate electrons that react with ketones to form ketyl radicals.