Activated complex
Encyclopedia
In chemistry
an activated complex is defined by the International Union of Pure and Applied Chemistry
as "that assembly of atoms which corresponds to an arbitrary infinitesimally small region at or near the col (saddle point) of a potential energy surface". In other words, it refers to a collection of intermediate structures in a chemical reaction
that persist while bonds
are breaking and new bonds are forming. It therefore represents not one defined state, but rather a range of transient configurations that a collection of atoms passes through in between clearly defined products and reactants.
It is the subject of transition state theory
- also known as activated complex theory - which studies the kinetics
of reactions that pass through a defined intermediate state with standard Gibbs free energy of formation
Δ‡ G °. The state represented by the double dagger symbol is known as the transition state
and represents the exact configuration that has an equal probability of forming either the reactants and products of the given reaction.
The activated complex is often confused with the transition state and is used interchangeably in many textbooks. However, it differs from the transition state in that the transition state represents only the highest potential energy configuration of the atoms during the reaction while the activated complex refers to all the configurations that the atoms pass through in the transformation from products to reactants. In terms of free energies, the activated complex represents all the energetic states in between the free energies of the reactants, the transition state, and the products. This can be visualized in terms of a reaction coordinate
, where the transition state is the molecular configuration at the peak of the diagram while the activated complex can refer to any point along the continuum.
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
an activated complex is defined by the International Union of Pure and Applied Chemistry
International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science . The international headquarters of IUPAC is located in Zürich,...
as "that assembly of atoms which corresponds to an arbitrary infinitesimally small region at or near the col (saddle point) of a potential energy surface". In other words, it refers to a collection of intermediate structures in a chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
that persist while bonds
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
are breaking and new bonds are forming. It therefore represents not one defined state, but rather a range of transient configurations that a collection of atoms passes through in between clearly defined products and reactants.
It is the subject of transition state theory
Transition state theory
Transition state theory explains the reaction rates of elementary chemical reactions. The theory assumes a special type of chemical equilibrium between reactants and activated transition state complexes....
- also known as activated complex theory - which studies the kinetics
Chemical kinetics
Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition...
of reactions that pass through a defined intermediate state with standard Gibbs free energy of formation
Gibbs free energy
In thermodynamics, the Gibbs free energy is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure...
Δ‡ G °. The state represented by the double dagger symbol is known as the transition state
Transition state
The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest energy along this reaction coordinate. At this point, assuming a perfectly irreversible reaction, colliding reactant molecules will always...
and represents the exact configuration that has an equal probability of forming either the reactants and products of the given reaction.
The activated complex is often confused with the transition state and is used interchangeably in many textbooks. However, it differs from the transition state in that the transition state represents only the highest potential energy configuration of the atoms during the reaction while the activated complex refers to all the configurations that the atoms pass through in the transformation from products to reactants. In terms of free energies, the activated complex represents all the energetic states in between the free energies of the reactants, the transition state, and the products. This can be visualized in terms of a reaction coordinate
Reaction coordinate
In chemistry, a reaction coordinate is an abstract one-dimensional coordinate which represents progress along a reaction pathway. It is usually a geometric parameter that changes during the conversion of one or more molecular entities....
, where the transition state is the molecular configuration at the peak of the diagram while the activated complex can refer to any point along the continuum.