Britannica Sources used in this answer

Why are free radicals important intermediates in some chemical reactions?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A graph showing a potential energy curve for a chemical reaction, with the y-axis labeled potential energy and the x-axis labeled progress of reaction. The curve rises from the initial state (reactants) to a peak labeled transition state (activated complex), indicating activation energy, then drops to the final state (products). — chemical kinetics In the Arrhenius equation, the activation energy (E) represents the minimum amount of energy required to transform reactants into products in a chemical reaction. On a potential energy curve, the value of the activation energy is equivalent to the difference in potential energy between particles in an intermediate configuration (known as the activated complex, or transition state) and particles of reactants in their initial state. The activation energy thus can be visualized as a barrier that must be overcome by reactants before products can be formed.

Free radicals are highly reactive, short-lived species that serve as essential transient intermediates in a wide variety of chemical processes, including combustion, thermal cracking, and many photochemical processes.

Their importance in chemical kinetics is primarily due to their role in chain reactions. In these processes, a radical acts as a reactive intermediate that is consumed in one step but regenerated in another. Because the radical is continually produced, a single initial radical can trigger the formation of many product molecules, significantly accelerating the overall reaction rate.

Beyond simple chain reactions, these intermediates are fundamental to:
* Polymerization: They are critical in the industrial manufacture of plastics and synthetic rubber.
* Organic Synthesis: They facilitate the halogenation of organic molecules and various other transformations in organic chemistry.
* Oxidation: They are involved in the reaction of molecular oxygen with numerous organic compounds.

While their concentrations are often too low for direct detection, their existence is confirmed through their rapid reactivity and the specific chemical products they generate.1