Electrophilic substitution reactions are
chemical reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
s in which an
electrophile
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively Electric charge, charged, have an ...
displaces a
functional group
In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
in a
compound, which is typically, but not always, aromatic. Aromatic substitution reactions are characteristic of
aromatic
In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated system, conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugati ...
compounds and are common ways of introducing functional groups into
benzene
Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...
rings. Some
aliphatic
In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated (in which all ...
compounds can undergo electrophilic substitution as well.
Electrophilic aromatic substitution
In electrophilic substitution in
aromatic compounds, an atom appended to the
aromatic ring, usually hydrogen, is replaced by an electrophile.
The most important reactions of this type that take place are
aromatic nitration,
aromatic halogenation,
aromatic sulfonation and
acylation and alkylating
Friedel-Crafts reactions.
It further consists of alkylation and acylation.
Electrophilic aliphatic substitution
In electrophilic substitution in
aliphatic
In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated (in which all ...
compounds, an electrophile displaces a functional group. This reaction is similar to
nucleophilic aliphatic substitution where the reactant is a nucleophile rather than an electrophile. The four possible electrophilic aliphatic substitution reaction mechanisms are S
E1, S
E2(front), S
E2(back) and S
Ei (Substitution Electrophilic), which are also similar to the nucleophile counterparts
SN1 and
SN2. In the S
E1 course of action the substrate first ionizes into a
carbanion and a positively charged organic residue. The carbanion then quickly recombines with the electrophile. The S
E2 reaction mechanism has a single
transition state
In chemistry, the transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. It is often marked w ...
in which the old bond and the newly formed bond are both present.
Electrophilic aliphatic substitution reactions are:
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Nitrosation
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Ketone halogenation
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Keto-enol tautomerism
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Aliphatic diazonium coupling
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Carbene insertion into C-H bonds
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Carbonyl alpha-substitution reactions
References
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{{Authority control
Substitution reactions