Chain propagation (sometimes referred to as propagation) is a process in which a
reactive intermediate
In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these comp ...
is continuously regenerated during the course of a
chemical chain reaction. For example, in the
chlorination Chlorination may refer to:
* Chlorination reaction
In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transform ...
of
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
, there is a two-step propagation cycle involving as chain carriers a chlorine atom and a
methyl radical
Methyl (also systematically named trihydridocarbon) is an organic compound with the chemical formula (also written as •). It is a metastable colourless gas, which is mainly produced ''in situ'' as a precursor to other hydrocarbons in the petrol ...
Chain reaction
IUPAC Gold Book which are regenerated alternately:
:•Cl + CH4 → HCl + •CH3
:•CH3 + Cl2 → CH3Cl + •Cl
The two steps add to give the equation for the overall chain reaction:
:CH4 + Cl2 → CH3Cl + HCl.
Polymerization
In a chain-growth polymerization reaction, the reactive end-group
End groups are an important aspect of polymer synthesis and characterization. In polymer chemistry, they are functional groups that are at the very ends of a macromolecule or oligomer (IUPAC). In polymer synthesis, like condensation polymerizati ...
s of a polymer chain react in each propagation step with a new monomer
In chemistry, a monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization.
Classification
Mo ...
molecule transferring the reactive group to the last unit. Here the chain carrier is the polymer molecule with a reactive end-group, and at each step it is regenerated with the addition of one monomer unit:
:
External links
* IUPAC Gold Book
The International Union of Pure and Applied Chemistry publishes many books which contain its complete list of definitions. The definitions are divided into seven "colour books": Gold, Green, Blue, Purple, Orange, White, and Red. There is also an e ...
definition
chain-propagating reaction
References
Chemical reactions
Polymer chemistry
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