Radical reactions can be initiated by light or by the presence of peroxides . These reactions are not sensible with the solvent polarity.
There are always three steps in radical reactions. A radical reaction involves the formation of a carbonyl radical. The radicals are formed by homolytic cleavage of a bond:
First step: boot
During this first step, there is the formation of an initiator radical which allows the following steps to occur. This radical comes from the homolytic cleavage of a bond. This operation needs an energy called “activation energy” and could provides:
- by the warmth (we give a kinetic energy to the molecules)
- or by photons hv: it’s a photochemical reaction.
- or by chemical way: the peroxides promote the formation of the radicals, it’s a thermochemical initiation.
Second step: propagation
This step occurs, generally, into two steps: the initiator radical previously formed reacts on the carbon substrate and leads to the formation of a new carbon radical. During this second step of propagation, the carbon radical reacts with a new reagent molecule.
Third step: termination or cessation
The radicals and the free atoms able to perform covalent bonds directly between them. The propagation of the chains generating radicals or atoms stops.