Radical reactions

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:

Untitled ACS Document 1996-3

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.

Untitled ACS Document 1996-3

  • or by chemical way: the peroxides promote the formation of the radicals, it’s a thermochemical initiation.

Untitled ACS Document 1996-3

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.


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