Preferred Label : transition state;
IUPAC definition : In theories describing elementary reactions it is usually assumed that there is a
transition state of more positive molar Gibbs energy between the reactants and the
products through which an assembly of atoms (initially composing the molecular entities
of the reactants) must pass on going from reactants to products in either direction.
In the formalism of 'transition state theory' the transition state of an elementary
reactions is that set of states (each characterized by its own geometry and energy)
in which an assembly of atoms, when randomly placed there, would have an equal probability
of forming the reactants or of forming the products of that elementary reactions.
The transition state is characterized by one and only one imaginary frequency. The
assembly of atoms at the transition state has been called an activated complex. (It
is not a complex according to the definition in this Compendium.) It may be noted
that the calculations of reaction rates by the transition state method and based on
calculated potential-energy surfaces refer to the potential energy maximum at the
saddle point, as this is the only point for which the requisite separability of transition
state coordinates may be assumed. The ratio of the number of assemblies of atoms that
pass through to the products to the number of those that reach the saddle point from
the reactants can be less than unity, and this fraction is the 'transmission coefficient'
κ. (There are also reactions, such as the gas-phase colligation of simple radicals,
that do not require 'activation' and which therefore do not involve a transition state.);
Origin ID : T06468;
Automatic exact mappings (from CISMeF team)
- See also
In theories describing elementary reactions it is usually assumed that there is a
transition state of more positive molar Gibbs energy between the reactants and the
products through which an assembly of atoms (initially composing the molecular entities
of the reactants) must pass on going from reactants to products in either direction.
In the formalism of 'transition state theory' the transition state of an elementary
reactions is that set of states (each characterized by its own geometry and energy)
in which an assembly of atoms, when randomly placed there, would have an equal probability
of forming the reactants or of forming the products of that elementary reactions.
The transition state is characterized by one and only one imaginary frequency. The
assembly of atoms at the transition state has been called an activated complex. (It
is not a complex according to the definition in this Compendium.) It may be noted
that the calculations of reaction rates by the transition state method and based on
calculated potential-energy surfaces refer to the potential energy maximum at the
saddle point, as this is the only point for which the requisite separability of transition
state coordinates may be assumed. The ratio of the number of assemblies of atoms that
pass through to the products to the number of those that reach the saddle point from
the reactants can be less than unity, and this fraction is the 'transmission coefficient'
κ. (There are also reactions, such as the gas-phase colligation of simple radicals,
that do not require 'activation' and which therefore do not involve a transition state.)
