composite mechanism

Also contains definition of: negative feedback
https://doi.org/10.1351/goldbook.C01210
A reaction that involves more than one @E02035@ is said to occur by a @CT07545@ mechanism. The terms @C01205@, @I03011@ mechanism, and @S05970@ mechanism are also commonly used. There are two main kinds of evidence for a @CT07545@ mechanism:
  1. The kinetic equation for the reaction does not correspond to its @S06026@.
  2. There is experimental evidence, direct or indirect, for intermediates of such a nature that it is necessary to conclude that more than one @E02035@ is involved.
There are many types of @CT07545@ mechanisms, for example:
  • Reactions occurring in parallel, such as:
    C01210-1.png
    C01210-2.png
    are called @P04403@ or @S05680@. When there are @S05680@ there is sometimes @C01198@, 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 @O04302@:
    C01210-5.png
  • Reactions occurring in @ST06775@, such as
    C01210-6.png
    are known as @C01276@.
  • 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 (@P04767@) or it may inhibit it (negative feedback).
  • @C00960@
    • Source:
    PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 161 [Terms] [Paper]
    Citation: 'composite mechanism' in IUPAC Compendium of Chemical Terminology, 3rd ed. International Union of Pure and Applied Chemistry; 2006. Online version 3.0.1, 2019. https://doi.org/10.1351/goldbook.C01210 RIS BibTex EndNote
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    Last revised: February 24, 2014