Electrophilic substitution reactions are
chemical reaction
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...
s in which an
electrophile displaces a
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the r ...
in a
compound, which is typically, but not always, aromatic. Aromatic substitution reactions are characteristic of
aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
compounds and are common ways of introducing functional groups into
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
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, like hexane ...
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 an ...
,
aromatic halogenation
In organic chemistry, an electrophilic aromatic halogenation is a type of electrophilic aromatic substitution. This organic reaction is typical of aromatic compounds and a very useful method for adding substituents to an aromatic system.
:
A few ...
,
aromatic sulfonation Aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution. Aryl sulfonic acids are used as detergents, dye, and drugs.
Stoichiometr ...
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, like hexane ...
compounds, an electrophile displaces a functional group. This reaction is similar to
nucleophilic aliphatic substitution
In chemistry, a nucleophilic substitution is a class of chemical reactions in which an electron-rich chemical species (known as a nucleophile) replaces a functional group within another electron-deficient molecule (known as the electrophile). Th ...
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 ...
in which the old bond and the newly formed bond are both present.
Electrophilic aliphatic substitution reactions are:
*
Nitrosation
*
Ketone halogenation
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Keto-enol tautomerism
*
Aliphatic diazonium coupling
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Carbene
In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms.
The term "carbene" m ...
insertion into C-H bonds
*
Carbonyl alpha-substitution reactions
References
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{{Authority control
Substitution reactions