Editing Substitution reaction (section)

{{short description|Chemical reaction in which one functional group in a compound is replaced by another}}
{{redirect|Aromatic substitution|''ortho/meta/para'' patterns|Arene substitution pattern}}
A '''substitution reaction''' (also known as '''single displacement reaction''' or '''single substitution reaction)''' is a chemical reaction during which one [[functional group]] in a [[chemical compound]] is replaced by another functional group.<ref name=":0">{{JerryMarch}}</ref> Substitution reactions are of prime importance in [[organic chemistry]]. Substitution reactions in organic chemistry are classified either as [[electrophile|electrophilic]] or [[nucleophile|nucleophilic]] depending upon the reagent involved, whether a [[reactive intermediate]] involved in the reaction is a [[carbocation]], a [[carbanion]] or a [[radical (chemistry)|free radical]], and whether the [[substrate (chemistry)|substrate]] is [[aliphatic]] or [[aromatic]]. Detailed understanding of a reaction type helps to predict the product outcome in a reaction. It also is helpful for optimizing a reaction with regard to variables such as temperature and choice of [[solvent]].

A good example of a substitution reaction is [[halogenation]]. When [[chlorine]] gas (Cl<sub>2</sub>) is irradiated, some of the molecules are split into two chlorine [[radical (chemistry)|radicals]] (Cl•), whose free electrons are strongly [[nucleophilic]]. One of them breaks a [[carbon–hydrogen bond|C–H covalent bond]] in CH<sub>4</sub> and grabs the hydrogen atom to form the electrically neutral HCl. The other radical reforms a covalent bond with the CH<sub>3</sub>• to form CH<sub>3</sub>Cl ([[methyl chloride]]).

{| class="wikitable" 
|- align="center" 
||
[[Image:SubstitutionReaction.svg|Substitution reaction : chlorination of methane]]
|- align="center"
!chlorination of methane by chlorine
|}