composite mechanism

Also contains definition of: negative feedback
https://doi.org/10.1351/goldbook.C01210
A reaction that involves more than one @[email protected] is said to occur by a @[email protected] mechanism. The terms @[email protected], @[email protected] mechanism, and @[email protected] mechanism are also commonly used. There are two main kinds of evidence for a @[email protected] mechanism:
  1. The kinetic equation for the reaction does not correspond to its @[email protected]
  2. There is experimental evidence, direct or indirect, for intermediates of such a nature that it is necessary to conclude that more than one @[email protected] is involved.
There are many types of @[email protected] mechanisms, for example:
  • Reactions occurring in parallel, such as:
    C01210-1.png
    C01210-2.png
    are called @[email protected] or @[email protected] When there are @[email protected] there is sometimes @[email protected], as in the scheme:
    C01210-3.png
    C01210-4.png
    where B and C compete with one another for A.
  • Reactions occurring in forward and reverse directions are called @[email protected]:
    C01210-5.png
  • Reactions occurring in @[email protected], such as
    C01210-6.png
    are known as @[email protected]
  • Reactions are said to exhibit feedback if a substance formed in one step affects the rate of a previous step. For example, in the scheme:
    C01210-6.png
    The intermediate Y may catalyse the reaction C01210-7.png (@[email protected]) or it may inhibit it (negative feedback).
  • @[email protected]
    • Source:
    PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 161 [Terms] [Paper]
    Cite as: IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S. J. Chalk. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.
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    Last revised: February 24, 2014