Chain propagation in the context of "Free-radical reaction"

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👉 Chain propagation in the context of Free-radical reaction

A free-radical reaction is any chemical reaction involving free radicals. This reaction type is abundant in organic reactions. Two pioneering studies into free radical reactions have been the discovery of the triphenylmethyl radical by Moses Gomberg (1900) and the lead-mirror experiment described by Friedrich Paneth in 1927. In this last experiment tetramethyllead is decomposed at elevated temperatures to methyl radicals and elemental lead in a quartz tube. The gaseous methyl radicals are moved to another part of the chamber in a carrier gas where they react with lead in a mirror film which slowly disappears.

When radical reactions are part of organic synthesis the radicals are often generated from radical initiators such as peroxides or azobis compounds. Many radical reactions are chain reactions with a chain initiation step, a chain propagation step and a chain termination step. Reaction inhibitors slow down a radical reaction and radical disproportionation is a competing reaction. Radical reactions occur frequently in the gas phase, are often initiated by light, are rarely acid or base catalyzed and are not dependent on polarity of the reaction medium. Reactions are also similar whether in the gas phase or solution phase.

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Chain propagation in the context of Reaction step

In chemistry, a reaction step of a chemical reaction is defined as: "An elementary reaction, constituting one of the stages of a stepwise reaction in which a reaction intermediate (or, for the first step, the reactants) is converted into the next reaction intermediate (or, for the last step, the products) in the sequence of intermediates between reactants and products". To put it simply, it is an elementary reaction which goes from one reaction intermediate to another or to the final product.

The mechanism of a given reaction is the sequence of steps involved in the reaction. For different reactions, the sequences vary greatly in complexity. An elementary reaction consists of a single step. Other reactions can have mechanisms of several consecutive steps; the examples in the article on Reaction mechanism have as many as six. Also more complicated mechanisms exist such as chain reaction which include a repeating cycle of steps in a chain propagation.

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