Activated complex

Activated complex (diagram)
A basic reaction coordinate diagram showing the activated complex at the height of the transition state location on the free energy vs extent of reaction plot.
In chemistry, activated complex is the high energy structure formed during the transition stage (see: transition state) of a chemical reaction, between the reactants going to products, characteristic of the configuration species at or near the saddle point of the potential energy surface. [1]

Overview
In 1929,
German-born American physicist Fritz London, seems to seems to have originated the concept with the the publication of his formula for the energy of interaction of three or four electrons, such as in the approach interaction between two noble gas atoms that attract each other at large distance, but at short distance are repellent. [4]

In the 1930s,
American chemistry Henry Eyring and colleagues developed an activated complex theory, which enables the rate constants in chemical reactions to be calculated using statistical thermodynamics,

The following is a simplified activated complex diagram for a combination reaction, showing reactants (A + B) equilibriating between the "activated complex" (A - - - B), and the products (AB):

A + B A - - - B AB

Each activated complex is associated with a specific activation energy, unique to each activated complex species in the mechanism.

The activated complex, according to Linus Pauling (1969) is said to have “a larger energy (enthalpy) value than the reactants”. [2]

History
The was developed by in the 1930s. [3]

References
1. Activation complex – IUPAC Goldbook
2. Pauling, Linus. (1969). General Chemistry (pg. 565). Dover.
3. (a) Daintith, John. (2004). Oxford Dictionary of Chemistry. Oxford University Press.
(b) Eyring, Henry. (1935). “The Activated Complex in Chemical Reactions” (abstract), J. Chem. Phys. Vol. 3, Issue 2, 107.
4. Snow, Richard and Eyring, Henry. (1957). “Activated Complex Energies” (abstract), J. Phys. Chem., 61 (1): 1-6.

External links
‚óŹ Activated complex – Wikipedia.
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