Tolman's rule states that, in a certain chemical reaction, the steps involve exclusively intermediates of 18- and 16 electron configuration. The rule is an extension of the
18-electron rule. This rule was proposed by American chemist
Chadwick A. Tolman
Chadwick Alma Tolman (October 1938 – April 6, 2024) was an American chemist. He obtained his B.S. in Chemistry from Massachusetts Institute of Technology. He earned his Ph.D. in Chemistry as a microwave spectroscopist from U.C. Berkeley under ...
.
As stated above, Tolman's rule, even for reactions that proceed via 2e
− steps, is incorrect because many reactions involve configurations of fewer than 16 e
−.
Many examples of homogeneous catalysis involving organometallic complexes involve shuttling of complexes between 16 and 18 electron configurations. 16-electron complexes often form adducts with
Lewis base
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
s and, if low-valent, undergo
oxidative addition.
:
Conversely, complexes of 18 electron configuration tend to dissociate ligands or undergo
reductive elimination:
:
See also
*
Electron counting
Electron counting is a formalism used for classifying compounds and for explaining or predicting electronic structure and bonding. Many rules in chemistry rely on electron-counting:
*Octet rule is used with Lewis structures for main group eleme ...
References
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Organometallic chemistry
Chemical bonding
Empirical laws
Eponyms