Radical Reactions

Free radicals have the potential to be both incredibly potent chemical agents and potentially dangerous pollutants due to their high reactivity. Free radicals have a natural predisposition to proceed in a chain reaction way, which contributes significantly to their potency. Initiation, propagation, and termination are the three separate stages of a radical chain reaction. The process that first produces a radical species is known as the initiation phase. Due to the enormous energy barriers involved, homolytic cleavage events—which occur most frequently—are extremely uncommon. To break through the energy barrier it is frequently essential to use heat, UV light, or a metal-containing catalyst. Chain reactions' "chain" component is described in the propagation phase. Once a reactive free radical has been produced, it can interact with stable molecules to produce additional reactive free radicals. These fresh free radicals then proceed to produce even more new free radicals, and so forth. Hydrogen abstraction and radical addition to double bonds are frequent steps in the propagation process. Two free radical species reacting with one another to create a stable, non-radical adduct is what causes chain termination. The low concentration of radical species and the low likelihood of two radicals colliding with one another make this event, despite its extreme thermodynamic downhill nature, extremely rare. As a result of entropic rather than enthalpic factors the Gibbs free energy barrier for this reaction is very high.