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SN2 reaction
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==E2 competition== A common [[side reaction]] taking place with S<sub>N</sub>2 reactions is [[elimination reaction|E2 elimination]]: the incoming anion can act as a base rather than as a nucleophile, abstracting a proton and leading to formation of the [[alkene]]. This pathway is favored with sterically hindered nucleophiles. Elimination reactions are usually favoured at elevated temperatures<ref>{{cite web|url=http://www.masterorganicchemistry.com/2012/09/10/elimination-reactions-are-favored-by-heat/|title=Elimination Reactions Are Favored By Heat β Master Organic Chemistry|website=www.masterorganicchemistry.com|access-date=13 April 2018}}</ref> because of increased [[entropy]]. This effect can be demonstrated in the gas-phase reaction between a [[phenolate]] and a simple [[alkyl halide|alkyl bromide]] taking place inside a [[mass spectrometer]]:<ref>''Gas Phase Studies of the Competition between Substitution and Elimination Reactions'' Scott Gronert [[Accounts of Chemical Research]]; '''2003'''; 36(11) pp 848 - 857; (Article) {{doi|10.1021/ar020042n}}</ref><ref>The technique used is [[electrospray ionization]] and because it requires charged reaction products for detection the nucleophile is fitted with an additional sulfonate anionic group, non-reactive and well separated from the other anion. The product ratio of substitution and elimination product can be measured from the intensity their relative molecular ions.</ref> :[[File:SN2 E2 gas phase competition.svg|center|650px|Competition experiment between SN2 and E2]] With [[ethyl bromide]], the reaction product is predominantly the substitution product. As [[steric hindrance]] around the electrophilic center increases, as with [[isobutyl]] bromide, substitution is disfavored and elimination is the predominant reaction. Other factors favoring elimination are the strength of the base. With the less basic [[benzoate]] substrate, isopropyl bromide reacts with 55% substitution. In general, gas phase reactions and solution phase reactions of this type follow the same trends, even though in the first, [[solvent effects]] are eliminated.
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