In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...
, an alkyl group is an
alkane
In organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms tha ...
missing one
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a
cycloalkane by removal of a hydrogen atom from a
ring and has the general formula .
Typically an alkyl is a part of a larger molecule. In
structural formulae, the symbol R is used to designate a generic (unspecified) alkyl group. The smallest alkyl group is
methyl, with the formula .
Related concepts
Alkylation is an important operation in refineries, for example in the production of high-octane gasoline.
Alkylating antineoplastic agents are a class of compounds that are used to treat cancer. In such case, the term alkyl is used loosely. For example,
nitrogen mustard
Nitrogen mustards are cytotoxic organic compounds with the chloroethylamine (Cl(CH2)2NR2) functional group. Although originally produced as chemical warfare agents, they were the first chemotherapeutic agents for treatment of cancer. Nitrogen ...
s are well-known alkylating agents, but they are not simple hydrocarbons.
In chemistry, alkyl is a group, a substituent, that is attached to other molecular fragments. For example,
alkyl lithium reagents have the empirical formula Li(alkyl), where alkyl = methyl, ethyl, etc. A ''dialkyl'' ether is an
ether with two alkyl groups, e.g., diethyl ether (O(C
2H
5)
2).
In medicinal chemistry
In
medicinal chemistry, the incorporation of alkyl chains into some
chemical compounds increases their
lipophilicity. This strategy has been used to increase the antimicrobial activity of
flavanones and
chalcones.
Alkyl cations, anions, and radicals
Usually, alkyl groups are attached to other atoms or groups of atoms. Free alkyls occur as neutral compounds, as anions, or as cations. The cations are called
carbocations. The anions are called
carbanions. The neutral alkyl
free radicals have no special name. Such species are usually encountered only as transient intermediates, but some are quite stable and can be "put into a bottle". Typically alkyl cations are generated using
super acids, alkyl anions are observed in the presence of strong bases, and alkyl radicals are generated by a
photochemical reaction. Alkyls are commonly observed in
mass spectrometry of
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s.
Nomenclature
Alkyls form
homologous series. The simplest series have the general formula C
''n''H
2''n''+1. Alkyls include ''
methyl'', (CH
3·), ''
ethyl'' (C
2H
5·), ''
propyl'' (C
3H
7·), ''
butyl'' (C
4H
9·), ''
pentyl'' (C
5H
11·), and so on. Alkyl groups that contain one ring have the formula C
''n''H
2''n''−1, e.g. cyclopropyl and cyclohexyl.
The naming convention is taken from
IUPAC nomenclature:
These names are used to name branched chained structures, for example
3-methylpentane:
The structure of
3-methylpentane is viewed as consisting of two parts. First, five atoms comprise the longest straight chain of
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...
centers. The parent five-carbon compound is named
pentane (highlighted blue). The methyl "substituent" or "group" is highlighted red. According to the usual rules of nomenclature, alkyl groups are included in the name of the molecule before the root, as in
methylpentane. This name is, however, ambiguous, as the methyl branch could be on various carbon atoms. Thus, the name is 3-methylpentane to avoid ambiguity: The 3- is because the methyl is attached to the third of the five carbon atoms.
If there is more than one of the same alkyl group attached to a chain, then the prefixes are used on the alkyl groups to indicate multiples (i.e., di, tri, tetra, etc.)
This compound is known as
2,3,3-trimethylpentane
2,3,3-Trimethylpentane is a chemical compound in the family of hydrocarbons which has a formula of C8H18. It is an isomer of octane
Octane is a hydrocarbon and an alkane with the chemical formula , and the condensed structural formula . Octane ...
. Here three identical alkyl groups attached to carbon atoms 2, 3, and 3. The numbers are included in the name to avoid ambiguity about the position of the groups, and "tri" indicates that there are three identical methyl groups. If one of the methyl groups attached to the third carbon atom were instead an ethyl group, then the name would be 3-ethyl-2,3-dimethylpentane. When there are different alkyl groups, they are listed in alphabetical order.
In addition, each position on an alkyl chain can be described according to how many other carbon atoms are attached to it. The terms
primary,
secondary,
tertiary
Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago.
The period began with the demise of the non- avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...
, and
quaternary refer to a carbon attached to one, two, three, or four other carbons respectively.
Etymology
The first named alkyl radical was ethyl, named so by
Liebig in 1833 from the German word "Äther" (which in turn had been derived from the Greek word "aither") (https://en.wiktionary.org/wiki/ether , i.e., the substance now known as diethyl ether) and the Greek word ύλη (
hyle), meaning "matter". This was followed by methyl (
Dumas and
Peligot in 1834, meaning "spirit of wood") and amyl (
Auguste Cahours in 1840). The word alkyl was introduced by
Johannes Wislicenus in or before 1882, based on the German word "Alkoholradikale" and then-common suffix -yl.
See also
*
Alkane
In organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms tha ...
*
Alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
*
Alkyne
*
Aryl
*
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
*
IUPAC nomenclature of organic chemistry
References
{{Authority control
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Substituents