Title: chain reaction
Long Title: IUPAC Gold Book - chain reaction
DOI: 10.1351/goldbook.C00960
Status: current

Definition
A reaction in which one or more reactive reaction intermediates (frequently radicals) are continuously regenerated, usually through a repetitive cycle of elementary steps (the 'propagation step'). For example, in the chlorination of methane by a radical mechanism, $\ce{Cl^{.}}$ is continuously regenerated in the chain propagation steps:   In chain polymerization reactions, reactive intermediates of the same types, generated in successive steps or cycles of steps, differ in relative molecular mass, as in: 

Related Terms
- chain branching: https://goldbook.iupac.org//terms/view/C00948
- chain polymerization: https://goldbook.iupac.org//terms/view/C00958
- chain transfer: https://goldbook.iupac.org//terms/view/C00963
- degenerate chain branching: https://goldbook.iupac.org//terms/view/D01557
- initiation: https://goldbook.iupac.org//terms/view/I03042
- intermediates: https://goldbook.iupac.org//terms/view/I03096
- mechanism: https://goldbook.iupac.org//terms/view/M03804
- relative molecular mass: https://goldbook.iupac.org//terms/view/R05271
- termination: https://goldbook.iupac.org//terms/view/T06274

Sources
- PAC, 1993, 65, 2291. 'Nomenclature of kinetic methods of analysis (IUPAC Recommendations 1993)' on page 2293 (https://doi.org/10.1351/pac199365102291)
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1094 (https://doi.org/10.1351/pac199466051077)
- PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 157 (https://doi.org/10.1351/pac199668010149)

Related Reference
- PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2179 (https://doi.org/10.1351/pac199062112167)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/C00960/html
- json: https://goldbook.iupac.org/terms/view/C00960/json
- xml: https://goldbook.iupac.org/terms/view/C00960/xml

Citation: Citation: 'chain reaction' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.C00960
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Accessed: 2026-04-20T19:27:48+00:00