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{{Short description|Short-lived molecule formed as a step of a chemical reaction}}

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.

{{Distinguish|Reaction intermediate}}

In [[chemistry]], a '''reactive intermediate''' or an '''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 can these compounds be isolated and stored, e.g. low temperatures, [[matrix isolation]]. When their existence is indicated, reactive intermediates can help explain how a chemical reaction takes place.<ref>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}}.</ref><ref>March Jerry; (1992). Advanced Organic Chemistry reactions, mechanisms and structure (4th ed.). New York: John Wiley & Sons {{ISBN|0-471-60180-2}}</ref><ref>{{cite book|last1=Gilchrist|first1=T. L.|title=Carbenes nitrenes and arynes|date=1966|publisher=Springer US|isbn=9780306500268}}</ref><ref>{{cite book|last1=Moss|first1=Robert A.|last2=Platz|first2=Matthew S.|last3=Jones, Jr.|first3=Maitland|title=Reactive intermediate chemistry|date=2004|publisher=Wiley-Interscience|___location=Hoboken, N.J.|isbn=9780471721499}}</ref>

Most chemical reactions takes more than one "step" to complete, and an reactive intermediate is an unstable product that only exists in one of the intermediate steps. 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

Most chemical reactions take more than one [[elementary step]] to complete, and a reactive intermediate is a high-energy, hence unstable, product that exists only in one of the intermediate steps. The series of steps together make a [[reaction mechanism]]. A reactive intermediate differs from a reactant or product or a simple [[reaction intermediate]] only in that it cannot usually be isolated but is sometimes observable only through fast [[spectroscopic]] methods. It is stable in the sense that an [[elementary reaction]] forms the reactive intermediate and the elementary reaction in the next step is needed to destroy it.

:A + 2B &rarr; C + D + E,

When a reactive intermediate is not observable, its existence must be [[inferred]] through experimentation. This usually involves changing reaction conditions such as temperature or concentration and applying the techniques of [[chemical kinetics]], [[chemical thermodynamics]], or [[spectroscopy]]. Reactive intermediates based on carbon are [[radical (chemistry)|radicals]], [[carbene]]s, [[carbocation]]s, [[carbanion]]s, [[aryne]]s, and [[carbyne]]s.

broken down to steps:

===commonCommon features===

:A + B &rarr; C + X

Reactive intermediates have several features in common:

:X &rarr; D + Y

* low [[concentration]] with respect to reaction substrate and final reaction product

:B + Y &rarr; E.

* with the exception of carbanions, these intermediates do not obey the [[octet rule|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 [[spectroscopy|spectroscopic]] means

* [[cage effect (chemistry)|cage effects]] have to be taken into account

* often stabilisation by [[conjugated system|conjugation]] or [[Resonance_structureResonance structure|resonance]]

* often difficult to distinguistdistinguish from a [[transition state]]

* prove existence by means of [[chemical trap|chemical trapping]]ping

==Carbon==

Here X and Y are intermediates.

<gallery perrow="5">

==The main carbon reactive intermediates.==

File:Radical metilo--methyl radical.svg|Radical

File:Carbene.svg| Carbene

File:Methyl cation.svg|Carbocation

File:碳负离子.svg|Carbanion

File:Carbyne quartet.svg|Carbyne

File:1,2-Didehydrobenzol.svg|Benzyne (an aryne)

</gallery>

Here==Other X and Y arereactive intermediates.==

based on [[carbon]]

*[[Carbenoid]]

*[[Ion-neutral complex]]

* [[carbocation|carbocations]]

*[[Enol#Enolates|Keto anions]]

* [[carbanion|carbanions]]

*[[Nitrene]]s

* [[free radical|free radicals]]

*[[Oxocarbenium]] ions

* [[carbene|carbenes]]

*[[Phosphinidenes]]

*[[Phosphoryl nitride]]

===common features===

*[[Tetrahedral intermediate]]s in [[carbonyl]] addition reactions

* low [[concentration]] with respect to reaction substrate and final reaction product

* with the exception of carbanions, these intermediates do not obey the [[octet rule|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 [[spectroscopy|spectroscopic]] means

* [[cage effect (chemistry)|cage effects]] have to be taken into account

* often stabilisation by [[conjugated system|conjugation]] or [[Resonance_structure|resonance]]

* often difficult to distinguist from a [[transition state]]

* prove existence by means of [[chemical trap|chemical trapping]]

== See also ==

==The other reactive intermediates.==

* [[Activated complex]]

* [[nitrene|nitrenesTransition state]]

* [[carbyne]]

* [[carbenoid]]

* [[aryne|arynes]]

==References==

{{reflist}}

==External links==

==References==

*{{Commonscat-inline|Reactive intermediates}}

{{Reaction mechanisms}}

[[Category:Reactive intermediates| ]]

*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.

[[Category:Reaction mechanisms]]

*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.

[[Category:Chemistry]]

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