Editing SN2 reaction (section)

{{short description|Organic chemistry reaction}}
{{Redirect|SN2|slush nitrogen, the mixture of solid and liquid nitrogen sometimes abbreviated as SN<sub>2</sub>|slush nitrogen}}
{{DISPLAYTITLE:S<sub>N</sub>2 reaction}}
[[File:SN2-MeSH-MeI-montage-3D-balls.png|thumb|right|[[Ball-and-stick model|Ball-and-stick representation]] of the S<sub>N</sub>2 reaction of [[methanethiol|CH<sub>3</sub>SH]] with [[iodomethane|CH<sub>3</sub>I]] yielding dimethylsulfonium. Note that the attacking group attacks from the backside of the leaving group]]

The '''bimolecular nucleophilic substitution''' ('''S<sub>N</sub>2''') is a type of [[reaction mechanism]] that is common in [[organic chemistry]]. In the S<sub>N</sub>2 reaction, a strong [[nucleophile]] forms a new bond to an [[orbital hybridisation|sp<sup>3</sup>]]-hybridised carbon atom via a backside attack, all while the [[leaving group]] detaches from the reaction center in a [[Concerted reaction|concerted]] (i.e. simultaneous) fashion.

The name S<sub>N</sub>2 refers to the [[Hughes-Ingold symbol]] of the mechanism:  "S<sub>N</sub>" indicates that the reaction is a [[nucleophilic substitution]], and "2" that it proceeds via a [[bimolecular]] mechanism, which means both the reacting species are involved in the [[rate-determining step]]. What distinguishes S<sub>N</sub>2 from the other major type of nucleophilic substitution, the [[SN1 reaction|S<sub>N</sub>1 reaction]], is that the displacement of the leaving group, which is the rate-determining step, is separate from the nucleophilic attack in S<sub>N</sub>1.

The S<sub>N</sub>2 reaction can be considered as an organic-chemistry analogue of the [[associative substitution]] from the field of [[inorganic chemistry]].