20.7:
Radical Formation: Elimination
Radical formation via the elimination process is the mechanistic reverse of the radical addition reaction. It occurs due to an unstable radical.
For instance, dibenzoyl peroxide undergoes homolysis to form a radical, which is unstable. So, it undergoes elimination to generate a phenyl radical and carbon dioxide.
The site of the unpaired electron in the radical is the α position. During the elimination reaction, the unstable radical cleaves the carbon–carbon σ bond at the β position to yield a stable radical.
Accordingly, there forms a double bond between the α and β positions, resulting in two product fragments—a radical species and an unsaturated molecule.
20.7:
Radical Formation: Elimination
Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions with respect to the radical, leading to the formation of an unsaturated molecule as the byproduct.
Figure 1. The elimination reaction of dibenzoyl peroxide for the formation of radicals.