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What are Radical initiators and their role in a free radical reaction?

Radical initiators are chemical species that quickly produce free radicals by light and heat exposure. Examples include Halogens (Cl2), AIBN (R-N=N-R), peroxides (R-O-O-R), acetophenone, benzophenone, etc.

These mild conditions provide enough energy equivalent to the bond dissociation energy. The internal bonds cleave easily and homolytically to produce free radicals. These radicals can then react with substrate molecules to initiate a series of chain reactions like polymerization or polyalkylation.

The peroxides and AIBN are thermal polymerization initiators. Photopolymerization initiators are benzophenone derivatives like Cl2, benzoin, acetophenone, etc.

 

What are free radical initiators? Examples

 

They also can induce homolytic bond cleavage and initiate radical reactions in other stable hydrocarbon reactant molecules like alkanes and alkenes. For example, a Chlorine molecule (Cl2), on exposure to ultraviolet light, generates two chlorine radicals (Cl•). These free radicals can initiate radical formation in alkanes and form polychlorinated alkanes.

 

Halogenation radical initiator alkane

The alkenes and free radicals form polymerization products like PVC, Teflon, etc.

 

Polymerization teflon radical initiator

Related Reading- Free Radicals (Introduction, Structure, and Types)

Reactive Intermediates
Organic Chemistry - Drawing Structures, Concepts, and Examples

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