Reaction intermediate

Reaction Intermediate

A Reaction intermediate is a molecular entity that is formed from the reactants (or preceding intermediates) and reacts further to give the directly observed products of a chemical reaction. Most chemical reactions are stepwise, that is they take more than one elementary step to complete. An intermediate is the reaction product of each of these steps, except for the last one, which forms the final product.

Formation and Consumption

Reaction intermediates are often free radicals or ions. The kinetics of a stepwise reaction are complex because they depend on the sequence of elementary steps that make up the reaction. For example, the rate equation for the reaction depends on the rate-determining step, i.e. it is determined by the slowest step in the sequence.

Stability

Reaction intermediates are often unstable and highly reactive. They are usually not isolated, but are detected by spectroscopic methods, or trapped in low-temperature matrices. They are also identified by their chemical kinetics behavior, for example by examining the kinetic isotope effect.

Examples

Examples of reaction intermediates include molecular ions in mass spectrometry, radicals in radical reactions, carbocations and carbanions in organic chemistry, and transition states in general. They also include enzyme-substrate complexes in biochemistry.

See also

• Transition state
• Chemical kinetics
• Free radical
• Ion
• Carbocation
• Carbanion
• Enzyme-substrate complex