In chemistry a reactive intermediate is a short-lived high energy highly reactive molecule. When generated in a chemical reaction it will quickly convert into a more stable molecule. Only in exceptional cases these compounds can be isolated and stored. Reactive intermediates help explain how a chemical reaction takes place.

Most chemical reactions take more than one elementary step to complete, and an reactive intermediate is an unstable product that only exists in one of the intermediate steps. The series of steps together make a reaction mechanism. It differs from the reactants and products in the way that it cannot be isolated, and is thus not directly observable. An example would be

A + 2B → C + D + E,

broken down to steps:

A + B → C + X

X → D + Y

B + Y → E.

Here X and Y are intermediates.

The main carbon reactive intermediates.

based on carbon

• carbocations
• carbanions
• free radicals
• carbenes

common features

• low concentration with respect to reaction substrate and final reaction product
• with the exception of carbanions, these intermediates do not obey the lewis octet rule hence the high reactivity
• often generated on chemical decomposition of a chemical compound
• it is often possible to prove the existence of this species by spectroscopic means
• cage effects have to be taken into account
• often stabilisation by conjugation or resonance
• often difficult to distinguish from a transition state
• prove existence by means of chemical trapping

The other reactive intermediates.

• nitrenes
• carbyne
• carbenoid
• arynes

References

• Carey, Francis A.; Sundberg, Richard J.; (1984). Advanced Organic Chemistry Part A Structure and Mechanisms (2nd ed.). New York N.Y.: Plenum Press. ISBN 0-306-41198-9.
• March Jerry; (1885). Advanced Organic Chemistry reactions, mechanisms and structure (3rd ed.). New York: John Wiley & Sons, inc. ISBN 0-471-85472-7
• Gilchrist T.C.;Rees C.W.; (1969) carbenes, nitrenes and arynes. Nelson. London.

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