Term: complex mechanism
https://doi.org/10.1351/goldbook.C01205

Definition:
This term is sometimes applied to an elementary reaction which proceeds via an intermediate species having a lifetime longer than a few rotational periods, in contrast to a direct reaction. However, in view of the danger of confusion with a reaction occurring in more than one step (a composite reaction) this usage is not to be recommended; it is better to use the terms complex-mode mechanism or complex-mode reaction.

Related Terms:
1) elementary reaction (http://doi.org/10.1351/goldbook.E02035).
2) direct reaction (http://doi.org/10.1351/goldbook.D01773).
3) composite reaction (http://doi.org/10.1351/goldbook.C01211).
4) mode (http://doi.org/10.1351/goldbook.M03958).
5) complex-mode reaction (http://doi.org/10.1351/goldbook.C01206).

Source: PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 160 (https://doi.org/10.1351/pac199668010149)

Citation: 'complex mechanism' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.C01205

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