20.6:
Radical Formation: Addition
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.
20.6:
Radical Formation: Addition
Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an unpaired electron if the reaction begins with a reactant having an unpaired electron.
The most facile category of radical formation via the addition process is reduction, where a single electron is added. The Birch reduction of organic compounds is one such example. It employs the electron generated as a metal of group 1 in the periodic table dissolves in liquid ammonia to form the corresponding stable M+1 ion.