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| {{Short description|Short-lived molecule formed as a step of a chemical reaction}}
| | #REDIRECT [[Reaction intermediate]] |
| {{Distinguish|Reaction intermediate}}
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| 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>
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| 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.
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| 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.
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| ==Common features==
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| Reactive intermediates have several features in common:
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| * low [[concentration]] with respect to reaction substrate and final reaction product
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| * with the exception of carbanions, these intermediates do not obey the [[octet rule|lewis octet rule]], hence the high reactivity
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| * often generated on [[chemical decomposition]] of a [[chemical compound]]
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| * it is often possible to prove the existence of this species by [[spectroscopy|spectroscopic]] means
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| * [[cage effect (chemistry)|cage effects]] have to be taken into account
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| * often stabilisation by [[conjugated system|conjugation]] or [[Resonance structure|resonance]]
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| * often difficult to distinguish from a [[transition state]]
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| * prove existence by means of [[chemical trap]]ping
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| ==Carbon==
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| <gallery perrow="5">
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| File:Radical metilo--methyl radical.svg|Radical
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| File:Carbene.svg| Carbene
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| File:Methyl cation.svg|Carbocation
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| File:碳负离子.svg|Carbanion
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| File:Carbyne quartet.svg|Carbyne
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| File:1,2-Didehydrobenzol.svg|Benzyne (an aryne)
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| </gallery>
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| ==Other reactive intermediates==
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| *[[Carbenoid]]
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| *[[Ion-neutral complex]]
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| *[[Enol#Enolates|Keto anions]]
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| *[[Nitrene]]s
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| *[[Oxocarbenium]] ions
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| *[[Phosphinidenes]]
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| *[[Phosphoryl nitride]]
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| *[[Tetrahedral intermediate]]s in [[carbonyl]] addition reactions
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| == See also ==
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| * [[Activated complex]]
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| * [[Transition state]]
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| ==References==
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| {{reflist}}
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| ==Extranol links==
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| *{{Commonscat-inline|Reactive intermediates}}
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| {{Reaction mechanisms}}
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| [[Category:Reactive intermediates| ]]
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| [[Category:Reaction mechanisms]]
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