Radical Reactions

Free radicals have a high degree of reactivity, which gives them the potential to be both very dangerous pollutants and very strong chemical weapons. Because radical processes naturally like to go in a chain reaction way, a large portion of the strength of free radical species comes from this trait. The start, propagation, and termination phases of a chain reaction involving radicals are all unique from one another. The first step that produces a radical species is referred to as the initiation phase. Because of the enormous energy barriers involved, this is often a homolytic cleavage event that only occurs extremely infrequently. To break through the energy barrier, it is frequently essential to use heat, UV light, or a catalyst that contains metal. The "chain" component of chain reactions is described by the propagation phase. Once a reactive free radical is created, it can combine with other stable molecules to create additional reactive free radicals. More free radicals are produced by these fresh ones, and so forth. Steps in the propagation process frequently include removing hydrogen from double bonds or adding the radical to them. When two free radical species interact with one another to create a stable, non-radical adduct, chain termination occurs. Due to the low concentration of radical species and the low probability of two radicals colliding, even though this is a very thermodynamically downhill event, it is also very uncommon. In other words, the Gibbs free energy barrier for this reaction is very high, primarily because of entropic rather than enthalpic factors.