Electrophilic substitution reactions are
chemical reactions in which an
electrophile displaces a
functional group in a
compound, which is typically, but not always, aromatic. Aromatic substitution reactions are characteristic of
aromatic compounds and are common ways of introducing functional groups into
benzene rings. Some
aliphatic 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
In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters between alcohols and ...
,
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 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
In organic chemistry, a carbanion is an anion in which carbon is trivalent (forms three bonds) and bears a formal negative charge (in at least one significant resonance form).
Formally, a carbanion is the conjugate base of a carbon acid:
:R3C ...
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 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