{{short description|Chemical reaction in which all bond reformation occurs in one step}} {{redirect|Concerted|the organization|Concerted (organization)}} [[File:Sn2EtCl+bromide.png|thumb|S{{sub|N}}2 reaction of a bromide ion with chloroethane showing the concerted nature of the reaction, the transition state and the predictable stereochemistry through Walden inversion.]]
In chemistry, a '''concerted reaction''' is a chemical reaction in which all bond breaking and bond making occurs in a single step. Reactive intermediates or other unstable high energy intermediates are not involved.<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>{{Cite journal|url = http://goldbook.iupac.org/CT07011.html|title = IUPAC Gold Book - concerted reaction|doi = 10.1351/goldbook.CT07011|date = 24 February 2014|accessdate = 12 April 2014|publisher = IUPAC|doi-access = free|url-access = subscription}}</ref> Concerted reaction rates tend not to depend on solvent polarity ruling out large buildup of charge in the transition state. The reaction is said to progress through a '''concerted mechanism''' as all bonds are formed and broken ''in concert''. Pericyclic reactions, the S{{sub|N}}2 reaction, and some rearrangements - such as the Claisen rearrangement - are concerted reactions.
The rate of the S<sub>N</sub>2 reaction is second order overall due to the reaction being bimolecular (i.e. there are two molecular species involved in the rate-determining step). The reaction does not have any intermediate steps, only a transition state. This means that all the bond making and bond breaking takes place in a single step. In order for the reaction to occur both molecules must be situated correctly.
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Category:Organic reactions