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In
chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a with other . ...

chemistry
, an alkene is a
hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structures, it is difficult to generalize furth ...
that contains a
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
–carbon
double bond In chemistry, a double bond is a between two s involving four s as opposed to two in a . Double bonds occur most commonly between two carbon atoms, for example in s. Many double bonds exist between two different elements: for example, in a group ...

double bond
. The term is often used as synonym of olefin, that is, any
hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structures, it is difficult to generalize furth ...
containing one or more double bonds.H. Stephen Stoker (2015):
General, Organic, and Biological Chemistry
'. 1232 pages.
However, the
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science Council (ISC). IUPAC ...
recommends using the name "alkene" only for acyclic hydrocarbons with just one double bond; alkadiene, alkatriene, etc., or polyene for acyclic hydrocarbons with two or more double bonds; cycloalkene, cycloalkadiene, etc. for cyclic ones; and "olefin" for the general class — cyclic or acyclic, with one or more double bonds. Acyclic alkenes, with only one double bond and no other
functional group In organic chemistry, a functional group is a 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 re ...
s (also known as mono-enes) form a
homologous seriesIn organic chemistry, a homologous series is a sequence In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order theory, order matters. Like a Set (mathematics), set, it contains Element (mathemati ...
of
hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structures, it is difficult to generalize furth ...
s with the general formula ''n''2''n'' with ''n'' being 2 or more (which is two
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
s less than the corresponding
alkane In , an alkane, or paraffin (a historical that also has ), is an . In other words, an alkane consists of and atoms arranged in a structure in which all the s are . Alkanes have the general chemical formula C''n''H2''n''+2. The alkanes rang ...
). When ''n'' is four or more, there are multiple
isomer In , isomers are s or s with identical s — that is, same number of of each — but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Isomers do not necessarily share similar or . Two main forms of ...

isomer
s with this formula, distinguished by the position and
conformation Conformation generally means structural arrangement and may refer to: * Conformational isomerism, a form of stereoisomerism in chemistry ** Carbohydrate conformation ** Cyclohexane conformation ** Protein conformation ** Conformation activity relat ...
of the double bond. Alkenes are generally colorless apolar compounds, somewhat similar to alkanes but more reactive. The first few members of the series are gases or liquids at room temperature. The simplest alkene,
ethylene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science C ...

ethylene
(C2H4) (or "ethene" in the
IUPAC nomenclature The International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a mem ...
) is the
organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
produced on the largest scale industrially.
Aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), planar (flat) structures with pi bonds in Resonance (che ...

Aromatic
compounds are often drawn as cyclic alkenes, but their structure and properties are sufficiently distinct that they are not classified as alkenes or olefins. Hydrocarbons with two overlapping double bonds (C=C=C) are called
allenes Allenes are organic compounds , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, catenat ...
—the simplest such compound is itself called ''
allene Allenes are organic compounds , CH4; is among the simplest organic compounds. In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, eleme ...
''—and those with three or more overlapping bonds (C=C=C=C, C=C=C=C=C, etc.) are called
cumulene A cumulene is a hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical ...
s. Some authors do not consider allenes and cumulenes to be "alkenes".


Structural isomerism

Alkenes having four or more
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
atoms can form diverse
structural isomers In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a ...
. Most alkenes are also isomers of
cycloalkanes In organic chemistry Organic chemistry is a branch of that studies the structure, properties and reactions of s, which contain in .Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . Stu ...

cycloalkanes
. Acyclic alkene structural isomers with only one double bond follow: * C2:
ethylene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science C ...

ethylene
only *C3:
propylene Propene, also known as propylene, is an unsaturated organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, comp ...

propylene
only *C4: 3 isomers: , , and
isobutylene Isobutylene (or 2-methylpropene) is a hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molec ...

isobutylene
*C5: 5 isomers: , 2-pentene, 2-methyl-1-butene, 3-methyl-1-butene,
2-methyl-2-butene 2-Methyl-2-butene, 2m2b, 2-methylbut-2-ene, also amylene is an alkene , the simplest alkene. In chemistry, an alkene is a hydrocarbon that contains a carbon–carbon double bond. The term is often used as synonym of olefin, that is, any hydr ...

2-methyl-2-butene
*C6: 13 isomers: , 2-hexene, 3-hexene,
methylpenteneMethylpentene is an alkene with a C6H12, molecular formula C6H12. The prefix "methyl-" is derived from the fact that there is a Methyl group, methyl(CH3) branch, the word root "-pent-" is derived from the fact that there are 5 carbon atoms in the par ...
(7 isomers), dimethylbutene (3 isomers) *C7: 27 isomers (calculated) *C12: 2,281 isomers (calculated) *C31: 193,706,542,776 isomers (calculated) Many of these molecules exhibit cis-trans isomerism. There may also be
chiral Chirality is a property of important in several branches of science. The word ''chirality'' is derived from the (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from its ; that is, i ...
carbons particularly within the larger molecules (from C5). The number of potential isomers increases rapidly with additional carbon atoms.


Structure


Bonding

Like a single
covalent bond A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they s ...
, double bonds can be described in terms of overlapping
atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of ato ...

atom
ic orbitals, except that, unlike a single bond (which consists of a single
sigma bond In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...

sigma bond
), a carbon–carbon double bond consists of one
sigma bond In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...

sigma bond
and one
pi bond In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
. This double bond is stronger than a single
covalent bond A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they s ...
(611 / mol for C=C vs. 347 kJ/mol for C–C) and also shorter, with an average
bond length Bond or bonds may refer to: Common meanings * Bond (finance) In finance Finance is the study of financial institutions, financial markets and how they operate within the financial system. It is concerned with the creation and management of ...
of 1.33
ångström The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.me ...

ångström
s (133 pm). Each carbon of the double bond uses its three sp2 hybrid orbitals to form sigma bonds to three atoms (the other carbon and two hydrogen atoms). The unhybridized 2p atomic orbitals, which lie perpendicular to the plane created by the axes of the three sp² hybrid orbitals, combine to form the pi bond. This bond lies outside the main C–C axis, with half of the bond on one side of the molecule and a half on the other. With a strength of 65 kcal/mol, the pi bond is significantly weaker than the sigma bond. Rotation about the carbon–carbon double bond is restricted because it incurs an energetic cost to break the alignment of the
p orbital In atomic theory Atomic theory is the scientific theory A scientific theory is an explanation of an aspect of the natural world and universe that can be repeatedly tested and verified in accordance with the scientific method The sc ...
s on the two carbon atoms. As a consequence, substituted alkenes may exist as one of two
isomer In , isomers are s or s with identical s — that is, same number of of each — but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Isomers do not necessarily share similar or . Two main forms of ...

isomer
s, called ''cis'' or ''trans'' isomers. More complex alkenes may be named with the ''E''–''Z'' notation for molecules with three or four different
substituent A substituent is one or a group of atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that ca ...
s (side groups). For example, of the isomers of butene, the two methyl groups of (''Z'')-but-2
-ene The suffix In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. The traditional areas of linguistic analy ...
(a.k.a. ''cis''-2-butene) appear on the same side of the double bond, and in (''E'')-but-2-ene (a.k.a. ''trans''-2-butene) the methyl groups appear on opposite sides. These two isomers of butene have distinct properties. Twisting to a 90° dihedral angle between two of the groups on the carbons requires less energy than the strength of a
pi bond In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
, and the bond still holds. The carbons of the double bond become
pyramidal A pyramid (from el, πυραμίς ') is a Nonbuilding structure, structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a Pyramid (geometry), pyramid in the geometric sense. The base of ...
, which allows preserving some
p orbital In atomic theory Atomic theory is the scientific theory A scientific theory is an explanation of an aspect of the natural world and universe that can be repeatedly tested and verified in accordance with the scientific method The sc ...
alignment—and hence pi bonding. The other two attached groups remain at a larger dihedral angle. This contradicts a common textbook assertion that the two carbons retain their planar nature when twisting, in which case the p orbitals would rotate enough away from each other to be unable to sustain a pi bond. In a 90°-twisted alkene, the p orbitals are only misaligned by 42° and the strain energy is only around 40 kcal/mol. In contrast, a fully broken pi bond has an energetic cost of around 65 kcal/mol. Some
pyramidal alkenePyramidal alkenes are alkene , the simplest alkene. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, str ...
s are stable. For example, ''trans''-
cycloocteneCyclooctene is the cycloalkene with an formula . Its molecule has a ring of 8 carbon atoms, connected by seven single bonds and one double bond. Cyclooctene is notable because it is the smallest cycloalkene that can exist as either the cis–trans ...

cyclooctene
is a stable strained alkene and the orbital misalignment is only 19°, despite having a significant
dihedral angle A dihedral angle is the angle between two intersecting planes or half-planes. In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, ele ...

dihedral angle
of 137° (a planar system has a dihedral angle of 180°) and a degree of pyramidalization of 18°. Even ''trans''- is stable at low temperatures.


Shape

As predicted by the
VSEPR Valence shell electron pair repulsion theory, or VSEPR theory ( , ), is a used in to predict the geometry of individual s from the number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm theory after its t ...
model of
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
pair repulsion, the
molecular geometry Molecular geometry is the arrangement of the s that constitute a . It includes the general shape of the molecule as well as s, bond angles, s and any other geometrical parameters that determine the position of each atom. Molecular geometry infl ...
of alkenes includes
bond angle Molecular geometry is the three-dimensional Three-dimensional space (also: 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called parameter A parameter (from the Ancient Greek language, Ancient Gre ...
s about each carbon in a double bond of about 120°. The angle may vary because of steric strain introduced by nonbonded interactions between
functional group In organic chemistry, a functional group is a 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 re ...
s attached to the carbons of the double bond. For example, the C–C–C bond angle in
propylene Propene, also known as propylene, is an unsaturated organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, comp ...

propylene
is 123.9°. For bridged alkenes, Bredt's rule states that a double bond cannot occur at the bridgehead of a bridged ring system unless the rings are large enough. Following Fawcett and defining ''S'' as the total number of non-bridgehead atoms in the rings, bicyclic systems require ''S'' ≥ 7 for stability and tricyclic systems require ''S'' ≥ 11.


Physical properties

Many of the physical properties of alkenes and
alkane In , an alkane, or paraffin (a historical that also has ), is an . In other words, an alkane consists of and atoms arranged in a structure in which all the s are . Alkanes have the general chemical formula C''n''H2''n''+2. The alkanes rang ...
s are similar: they are colorless, nonpolar, and combustible. The physical state depends on
molecular mass The molecular mass (''m'') is the mass of a given molecule: it is measured in dalton Dalton may refer to: Science * Dalton (crater), a lunar crater * Dalton (program), chemistry software * Dalton (unit) (Da), the atomic mass unit Entertainmen ...
: like the corresponding saturated hydrocarbons, the simplest alkenes (
ethylene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science C ...

ethylene
,
propylene Propene, also known as propylene, is an unsaturated organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, comp ...

propylene
, and
butene Butene, also known as butylene, is an alkene , the simplest alkene. In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that ...
) are gases at room temperature. Linear alkenes of approximately five to sixteen carbons are liquids, and higher alkenes are waxy solids. The melting point of the solids also increases with increase in molecular mass. Alkenes generally have stronger smells than their corresponding alkanes. Ethylene has a sweet and musty odor. The binding of cupric ion to the olefin in the mammalian olfactory receptor MOR244-3 is implicated in the smell of alkenes (as well as thiols). Strained alkenes, in particular, like norbornene and are known to have strong, unpleasant odors, a fact consistent with the stronger π complexes they form with metal ions including copper.


Reactions

Alkenes are relatively stable compounds, but are more reactive than
alkane In , an alkane, or paraffin (a historical that also has ), is an . In other words, an alkane consists of and atoms arranged in a structure in which all the s are . Alkanes have the general chemical formula C''n''H2''n''+2. The alkanes rang ...
s, either because of the reactivity of the carbon–carbon pi-bond or the presence of
allylic An allyl group is a substituent with the structural formula H2C=CH−CH2R, where R is the rest of the molecule. It consists of a methylene bridge (−CH2−) attached to a vinyl group (−CH=CH2). The name is derived from the Latin word for garlic, ...
CH centers. Most reactions of alkenes involve additions to this pi bond, forming new . Alkenes serve as a feedstock for the
petrochemical industry The petrochemical industry is concerned with the production and trade of petrochemicals Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum Petroleum (), also known as crude oil and oil, is a ...
because they can participate in a wide variety of reactions, prominently polymerization and alkylation.


Addition reactions

Alkenes react in many
addition reactionImage:Chlorine addition to ethene.svg, Addition of chlorine to ethylene An addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one (the adduct).. Addition reacti ...

addition reaction
s, which occur by opening up the double-bond. Most of these addition reactions follow the mechanism of
electrophilic addition . In organic chemistry, an electrophilic addition reaction is an addition reaction where a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of ...
. Examples are
hydrohalogenationA hydrohalogenation reaction is the electrophilic addition of hydrohalic acids like hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colo ...

hydrohalogenation
,
halogenation In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, ...

halogenation
, halohydrin formation, ,
hydroboration In chemistry, hydroboration refers to the addition of a hydrogen-boron bond to C-C, C-N, and C-O double bonds, as well as C-C triple bonds. This chemical reaction is useful in the organic synthesis of organic compounds. The development of this tech ...
, dichlorocarbene addition,
Simmons–Smith reaction The Simmons–Smith reaction is an organic reaction, organic cheletropic reaction involving an organozinc compound, organozinc carbenoid that reacts with an alkene (or alkyne) to form a cyclopropane. It is named after Howard Ensign Simmons, Jr. and ...
,
catalytic hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant ...
,
epoxidation An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle In geometry, an equilateral triangle is a triangle in which all three sides have the same length. In the familiar Euclidean geometry, an equilat ...

epoxidation
,
radical polymerizationFree-radical polymerization (FRP) is a method of polymerization, by which a polymer forms by the successive addition of free-radical building blocks. Free radicals can be formed by a number of different mechanisms, usually involving separate initiato ...
and
hydroxylation In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...
. :


Hydrogenation and related hydroelementations

Hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant ...

Hydrogenation
of alkenes produces the corresponding
alkane In , an alkane, or paraffin (a historical that also has ), is an . In other words, an alkane consists of and atoms arranged in a structure in which all the s are . Alkanes have the general chemical formula C''n''H2''n''+2. The alkanes rang ...
s. The reaction is sometimes carried out under pressure and at elevated temperature. Metallic
catalyst Catalysis () is the process of increasing the rate of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In cla ...

catalyst
s are almost always required. Common industrial catalysts are based on
platinum Platinum is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical el ...

platinum
,
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
, and
palladium Palladium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

palladium
. A large scale application is the production of
margarine Margarine (, also , ) is a spread used for flavoring, baking and cooking. It is most often used as a substitute for butter. Although originally made from animal fats, most margarine consumed today is made from vegetable oil. The foodstuff was or ...

margarine
. Aside from the addition of H-H across the double bond, many other H-X's can be added. These processes are often of great commercial significance. One example is the addition of H-SiR3, i.e.,
hydrosilylationHydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds."Hydrosilylation A Comprehensive Review on Recent Advances" B. Marciniec (ed.), Advances in Silicon Science, Springer Science, 2009. ...

hydrosilylation
. This reaction is used to generate
organosilicon compound Organosilicon compounds are organometallic compounds containing carbon–silicon chemical bond, bonds. Organosilicon chemistry is the corresponding science of their preparation and properties. Most organosilicon compounds are similar to the ordina ...
s. Another reaction is
hydrocyanation Hydrocyanation is the addition of hydrogen, H+ and cyanide, –CN to Substrate (chemistry), substrate. Usually the substrate is an alkene and the product is a nitrile. Hydrocyanation of unactivated alkenes Industrially, hydrocyanation is comm ...

hydrocyanation
, the addition of H-CN across the double bond.


Hydration

Hydration, the addition of water across the double bond of alkenes, yields
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...

alcohol
s. The reaction is catalyzed by
phosphoric acid Phosphoric acid, also known as orthophosphoric acid or phosphoric(V) acid, is a weak acid with the chemical formula . The pure compound is a colorless solid. All three hydrogens are acidic to varying degrees and can be lost from the molecule ...

phosphoric acid
or
sulfuric acid Sulfuric acid (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography English orthogra ...

sulfuric acid
. This reaction is carried out on an industrial scale to produce synthetic
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
. :CH2=CH2 + H2O → CH3–CH2OH Alkenes can also be converted into alcohols via the oxymercuration–demercuration reaction , the hydroboration–oxidation reaction or by .


Halogenation

In
electrophilic halogenationIn organic chemistry, an electrophilic aromatic halogenation is a type of electrophilic aromatic substitutionElectrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic ring, aromatic system (usually h ...
the addition of elemental
bromine Bromine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elemen ...

bromine
or
chlorine Chlorine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemica ...

chlorine
to alkenes yields vicinal dibromo- and dichloroalkanes (1,2-dihalides or ethylene dihalides), respectively. The decoloration of a solution of bromine in water is an analytical test for the presence of alkenes: :CH2=CH2 + Br2 → BrCH2–CH2Br Related reactions are also used as quantitative measures of unsaturation, expressed as the
bromine number Bromine number is the amount of bromine Bromine is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting ...
and
iodine number Iodine is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...
of a compound or mixture.


Hydrohalogenation

HydrohalogenationA hydrohalogenation reaction is the electrophilic addition of hydrohalic acids like hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colo ...

Hydrohalogenation
is the addition of
hydrogen halideHydrogen halides are diatomic Diatomic molecules are molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically ...
s, such as
HCl The hydrogen chloride has the and as such is a . At , it is a colourless , which forms white fumes of upon contact with atmospheric . Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, th ...

HCl
or HI, to alkenes to yield the corresponding
haloalkane The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from ...
s: :–CH= + HI → –CHI−–H If the two carbon atoms at the double bond are linked to a different number of hydrogen atoms, the halogen is found preferentially at the carbon with fewer hydrogen substituents. This patterns is known as
Markovnikov's rule In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...

Markovnikov's rule
. The use of
radical initiators Radical may refer to: Arts and entertainment Music *Radical (mixtape), ''Radical'' (mixtape), by Odd Future, 2010 *Radical (Smack album), ''Radical'' (Smack album), 1988 *"Radicals", a song by Tyler, The Creator from the 2011 album ''Goblin (album ...
or other compounds can lead to the opposite product result.
Hydrobromic acid Hydrobromic acid is a strong acid Acid strength is the tendency of an acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of forming a with an (a ). The first category of acids are the pr ...

Hydrobromic acid
in particular is prone to forming radicals in the presence of various impurities or even atmospheric oxygen, leading to the reversal of the Markovnikov result: :–CH= + HBr → –CHH––Br


Halohydrin formation

Alkenes react with water and halogens to form
halohydrin In organic chemistry a halohydrin (also a haloalcohol or β-halo alcohol) is a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic ch ...

halohydrin
s by an addition reaction. and anti-stereochemistry occur. : CH2=CH2 + X2 + H2O → XCH2–CH2OH + HX


Oxidation

Alkenes react with percarboxylic acids and even hydrogen peroxide to yield
epoxide An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle, which makes it ring strain, strained, and hence highly reactive, more so than other ethers. They are produced on a large scale for many applicat ...

epoxide
s: :RCH=CH2 + RO2H → RCHOCH2 + RO2H For ethylene, the
epoxidation An epoxide is a cyclic ether with a three-atom ring. This ring approximates an equilateral triangle In geometry, an equilateral triangle is a triangle in which all three sides have the same length. In the familiar Euclidean geometry, an equilat ...

epoxidation
is conducted on a very large scale industrially. This commercial route uses oxygen in the presence of catalysts: :C2H4 + 1/2 O2 → C2H4O Alkenes react with ozone, leading to the scission of the double bond. The process is called
ozonolysis Ozonolysis is an organic reaction where the Saturated and unsaturated compounds, unsaturated bonds of alkenes, alkynes, or azo compounds are Bond cleavage, cleaved with ozone. Alkenes and alkynes form organic compounds in which the multiple carbon ...

ozonolysis
. Often the reaction procedure includes an mild reductant, such as dimethylsulfide (SMe2): :RCH=CHR' + O3 + SMe2 → RCHO + R'CHO + O=SMe2 :R2C=CHR' + O3 → R2CHO + R'CHO + O=SMe2 When treated with a hot concentrated, acidified solution of , alkenes are cleaved
ketone In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence i ...
s and/or
carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...
s. The stoichiometry of the reaction is sensitive to conditions. This reaction and the ozonolysis can be used to determine the position of a double bond in an unknown alkene. The oxidation can be stopped at the vicinal
diol A diol is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical ...

diol
rather than full cleavage of the alkene by using
osmium tetroxide Osmium tetroxide (also osmium(VIII) oxide) is the chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass ...

osmium tetroxide
or other oxidants: :R'CH=CR2 + 1/2 O2 + H2O → R'CH(OH)-C(OH)R2 This reaction is called
dihydroxylationDihydroxylation is the process by which an alkene is converted into a vicinal (chemistry), vicinal diol. Although there are many routes to accomplish this oxidation, the most common and direct processes use a high-oxidation-state transition metal (t ...

dihydroxylation
. In the presence of an appropriate photosensitiser, such as
methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye 300px, Yarn drying after being dyed in the early American tradition, at Conner Prairie living history museum. A dye is a wiktionary:colored, colored substance ...

methylene blue
and light, alkenes can undergo reaction with reactive oxygen species generated by the photosensitiser, such as
hydroxyl radical The hydroxyl radical is the diatomic molecule . The hydroxyl radical is very stable as a dilute gas, but it decays very rapidly in the condensed phase. It is pervasive in some situations. Most notably the hydroxyl radicals is produced from the d ...

hydroxyl radical
s,
singlet oxygen Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with the formula O=O (also written as or ), which is in a quantum state where all electrons are spin paired. It is kinetically unstable at ambie ...
or
superoxide A superoxide is a compound that contains the superoxide ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space ...

superoxide
ion. Reactions of the excited sensitizer can involve electron or hydrogen transfer, usually with a reducing substrate (Type I reaction) or interaction with oxygen (Type II reaction). These various alternative processes and reactions can be controlled by choice of specific reaction conditions, leading to a wide range of products. A common example is the +2
cycloadditionA cycloaddition is a chemical reaction, in which "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." The resulting reaction is a ...
of singlet oxygen with a
diene In organic chemistry Organic chemistry is a branch of that studies the structure, properties and reactions of s, which contain in .Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . ...

diene
such as
cyclopentadiene Cyclopentadiene is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules ...

cyclopentadiene
to yield an
endoperoxide Image:Perester-2D-skeletal.png, 150px, The general structure of a perester Organic peroxides are organic compounds containing the peroxide functional group (ROOR′). If the R′ is hydrogen, the compounds are called organic hydroperoxides. Perester ...
: Another example is the Schenck ene reaction, in which singlet oxygen reacts with an
allyl An allyl group is a substituent with the structural formula H2C=CH−CH2R, where R is the rest of the molecule. It consists of a methylene bridge (−CH2−) attached to a vinyl group (−CH=CH2). The name is derived from the Latin word for garlic, ...

allyl
ic structure to give a transposed allyl
peroxide Peroxides are a group of compounds with the structure R−O−O−R, where R = any element. The O−O group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen ...

peroxide
:


Polymerization

Polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer, monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks.Clayden, J ...
of alkenes is a reaction that yields
polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its subsidiaries: ** Poly Property, a Hong Kong inc ...

polymer
s of high industrial value at great economy, such as the plastics
polyethylene Polyethylene or (incorrectly) polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most common plastic in use today. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and container ...

polyethylene
and
polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic A thermoplastic, or thermosoft plastic, is a plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermo ...

polypropylene
. Polymers from alkene
monomer In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...

monomer
s are referred to in a general way as ''
polyolefin A polyolefin is a type of polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat uni ...
s'' or in rare instances as ''polyalkenes''. A polymer from
alpha-olefin Alpha-olefins (or α-olefins) are a family of organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds comp ...
s is called a polyalphaolefin (PAO). Polymerization can proceed via either a free-
radical Radical may refer to: Arts and entertainment Music *Radical (mixtape), ''Radical'' (mixtape), by Odd Future, 2010 *Radical (Smack album), ''Radical'' (Smack album), 1988 *"Radicals", a song by Tyler, The Creator from the 2011 album ''Goblin (album ...
or an ionic mechanism, converting the double to a single bond and forming single bonds to join the other monomers. Polymerization of conjugated
diene In organic chemistry Organic chemistry is a branch of that studies the structure, properties and reactions of s, which contain in .Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . ...

diene
s such as
buta-1,3-diene 1,3-Butadiene (/ˌbjuːtəˈdʌɪiːn/) is the organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of ...

buta-1,3-diene
or
isoprene Isoprene, or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=C(CH3)−CH=CH2. In its pure form it is a colorless volatile liquid. Isoprene is an unsaturated hydrocarbon. It is produced by many plants and animals (includi ...

isoprene
(2-methylbuta-1,3-diene) results in largely 1,4-addition with possibly some 1,2-addition of the diene monomer to a growing polymer chain.


Metal complexation

: Alkenes are
ligand In coordination chemistry A coordination complex consists of a central atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havi ...
s in transition metal alkene complexes. The two carbon centres bond to the metal using the C–C pi- and pi*-orbitals. Mono- and diolefins are often used as ligands in stable complexes.
Cyclooctadiene A cyclooctadiene (sometimes abbreviated COD) is any of several cyclic diene with the formula (CH2)4(C2H2)2. Focusing only on cis derivatives, four isomer In chemistry Chemistry is the scientific discipline involved with Chemical element, el ...
and are popular chelating agents, and even
ethylene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science C ...

ethylene
itself is sometimes used as a ligand, for example, in Zeise's salt. In addition, metal–alkene complexes are intermediates in many metal-catalyzed reactions including hydrogenation, hydroformylation, and polymerization.


Reaction overview


Synthesis


Industrial methods

Alkenes are produced by hydrocarbon cracking. Raw materials are mostly
natural gas condensate Natural-gas condensate, also called natural gas liquids, is a low-density mixture of hydrocarbon In , a hydrocarbon is an consisting entirely of and . Hydrocarbons are examples of s. Hydrocarbons are generally colourless and hydrophobic with ...
components (principally ethane and propane) in the US and Mideast and
naphtha Naphtha ( or ) is a flammable liquid hydrocarbon mixture. Mixtures labelled ''naphtha'' have been produced from natural gas condensate Natural-gas condensate, also called natural gas liquids, is a low-density mixture of hydrocarbon In , a ...
in Europe and Asia. Alkanes are broken apart at high temperatures, often in the presence of a
zeolite Zeolites are microporous, aluminosilicate Aluminosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Ear ...

zeolite
catalyst, to produce a mixture of primarily aliphatic alkenes and lower molecular weight alkanes. The mixture is feedstock and temperature dependent, and separated by fractional distillation. This is mainly used for the manufacture of small alkenes (up to six carbons). Related to this is catalytic
dehydrogenation Dehydrogenation is the a chemical reaction that involves the removal of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest elem ...
, where an alkane loses hydrogen at high temperatures to produce a corresponding alkene. This is the reverse of the
catalytic hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant ...
of alkenes. This process is also known as reforming. Both processes are endothermic and are driven towards the alkene at high temperatures by
entropy Entropy is a scientific concept as well as a measurable physical property that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamic ...

entropy
.
Catalytic that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules ...
synthesis of higher α-alkenes (of the type RCH=CH2) can also be achieved by a reaction of ethylene with the
organometallic compound Organometallic chemistry is the study of organometallic compounds, chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any subst ...

organometallic compound
triethylaluminium Triethylaluminium is one of the simplest examples of an Organoaluminium chemistry, organoaluminium compound. Despite its name it has the Chemical formula, formula aluminum, Al2(Ethyl group, C2H5)6 (abbreviated as Al2Et6 or TEA), as it exists as a Di ...

triethylaluminium
in the presence of
nickel Nickel is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

nickel
,
cobalt Cobalt is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

cobalt
, or
platinum Platinum is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical el ...

platinum
.


Elimination reactions

One of the principal methods for alkene synthesis in the laboratory is the room
elimination Elimination may refer to: Science and medicine *Elimination reaction, an organic reaction in which two functional groups split to form an organic product *Bodily waste elimination, discharging feces, urine, or foreign substances from the body v ...

elimination
of alkyl halides, alcohols, and similar compounds. Most common is the β-elimination via the E2 or E1 mechanism, but α-eliminations are also known. The E2 mechanism provides a more reliable β-elimination method than E1 for most alkene syntheses. Most E2 eliminations start with an alkyl halide or alkyl sulfonate ester (such as a
tosylate A toluenesulfonyl (shortened tosyl, abbreviated TsNot to be confused with the synthetic element tennessine or Tos) group, H3CC6H4SO2, is a univalent organic group that consists of a Toluene, tolyl group, H3CC6H4, joined to a sulfonyl group, SO2, wi ...
or
triflate Triflate, also known by the systematic name trifluoromethanesulfonate, is a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemica ...

triflate
). When an alkyl halide is used, the reaction is called a
dehydrohalogenation Dehydrohalogenation is an elimination reaction that eliminates (removes) a hydrogen halide from a substrate (chemistry), substrate. The reaction is usually associated with the synthesis of alkenes, but it has wider applications. Dehydrohalogenation ...
. For unsymmetrical products, the more substituted alkenes (those with fewer hydrogens attached to the C=C) tend to predominate (see
Zaitsev's ruleIn organic chemistry, Zaitsev's rule (or Saytzeff's rule, Saytzev's rule) is an empirical rule for predicting the favored alkene , the simplest alkene. In chemistry Chemistry is the scientific discipline involved with Chemical element, e ...

Zaitsev's rule
). Two common methods of elimination reactions are dehydrohalogenation of alkyl halides and dehydration of alcohols. A typical example is shown below; note that if possible, the H is ''anti'' to the leaving group, even though this leads to the less stable ''Z''-isomer. Alkenes can be synthesized from alcohols via
dehydration In physiology, dehydration is a lack of total body water In physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studie ...
, in which case water is lost via the E1 mechanism. For example, the dehydration of
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
produces ethylene: :CH3CH2OH → H2C=CH2 + H2O An alcohol may also be converted to a better leaving group (e.g.,
xanthate 150px, Sodium salt of ethyl xanthate Xanthate usually refers to a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as ...

xanthate
), so as to allow a milder ''syn''-elimination such as the and the . Related reactions include eliminations by β-haloethers (the Boord olefin synthesis) and esters (). Alkenes can be prepared indirectly from alkyl
amine In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

amine
s. The amine or ammonia is not a suitable leaving group, so the amine is first either
alkylated Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene (or their equivalents). An alkyl group is a piece of a molecule with the ...

alkylated
(as in the
Hofmann elimination Hofmann elimination is an elimination reaction frame, Elimination reaction of cyclohexanol to cyclohexene with sulfuric acid">cyclohexene.html" ;"title="cyclohexanol to cyclohexene">cyclohexanol to cyclohexene with sulfuric acid and heat An elim ...

Hofmann elimination
) or oxidized to an
amine oxide An amine oxide, also known as amine-''N''-oxide and ''N''-oxide, is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than ...

amine oxide
(the Cope reaction) to render a smooth elimination possible. The Cope reaction is a ''syn''-elimination that occurs at or below 150 °C, for example: The Hofmann elimination is unusual in that the ''less'' substituted (non-) alkene is usually the major product. Alkenes are generated from α-halo
sulfone A sulfone is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical ...

sulfone
s in the Ramberg–Bäcklund reaction, via a three-membered ring sulfone intermediate.


Synthesis from carbonyl compounds

Another important method for alkene synthesis involves construction of a new carbon–carbon double bond by coupling of a carbonyl compound (such as an
aldehyde Chemically, an aldehyde is a compound containing a functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same ...

aldehyde
or
ketone In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence i ...
) to a
carbanionA carbanion is an anion An ion () is a particle, atom or molecule with a net electric charge, electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged ...
equivalent. Such reactions are sometimes called ''olefinations''. The most well-known of these methods is the
Wittig reaction The Wittig reaction or Wittig olefination is a chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classica ...

Wittig reaction
, but other related methods are known, including the
Horner–Wadsworth–Emmons reaction The Horner–Wadsworth–Emmons (HWE) reaction is a chemical reaction used in organic chemistry of stabilized phosphonate carbanions with aldehydes (or ketones) to produce predominantly E-alkenes. In 1958, Leopold Horner published a modified W ...
. The Wittig reaction involves reaction of an aldehyde or ketone with a
Wittig reagentIn organic chemistry, Wittig reagents are organophosphorus compound Organophosphorus compounds are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain ...
(or phosphorane) of the type Ph3P=CHR to produce an alkene and Ph3P=O. The Wittig reagent is itself prepared easily from
triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to Phosphorus, PPhenyl group, Ph3 or Ph3P. It is widely used in the synthesis of organic compound, organic an ...

triphenylphosphine
and an alkyl halide. The reaction is quite general and many functional groups are tolerated, even esters, as in this example: Related to the Wittig reaction is the Peterson olefination, which uses silicon-based reagents in place of the phosphorane. This reaction allows for the selection of ''E''- or ''Z''-products. If an ''E''-product is desired, another alternative is the
Julia olefination The Julia olefination (also known as the Julia–Lythgoe olefination) is the chemical reaction used in organic chemistry of phenyl sulfones (1) with aldehydes (or ketones) to give alkenes (olefins)(3) after alcohol functionalization and reductive e ...

Julia olefination
, which uses the carbanion generated from a
phenyl In organic chemistry Organic chemistry is a branch of that studies the structure, properties and reactions of s, which contain in .Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . Stu ...
sulfone A sulfone is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical ...

sulfone
. The
Takai olefination Takai olefination in organic chemistry describes the organic reaction of an aldehyde with a diorganochromium, diorganochromium compound to form an alkene. It is a name reaction, referencing Kazuhiko Takai, who first reported it in 1986. In the orig ...

Takai olefination
based on an organochromium intermediate also delivers E-products. A titanium compound,
Tebbe's reagent Tebbe's reagent is the organometallic compound with the formula (C5H5)2TiCH2ClAl(CH3)2. It is used in the methylenation of carbonyl In organic chemistry, a carbonyl group is a functional group In organic chemistry, a functional group is a ...
, is useful for the synthesis of methylene compounds; in this case, even esters and amides react. A pair of ketones or aldehydes can be deoxygenated to generate an alkene. Symmetrical alkenes can be prepared from a single aldehyde or ketone coupling with itself, using
titanium Titanium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...

titanium
metal reduction (the
McMurry reaction The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to form an alkene using a titanium chloride compound such as titanium(III) chloride and a reducing agent. The reaction is named after its co-discoverer, ...

McMurry reaction
). If different ketones are to be coupled, a more complicated method is required, such as the Barton–Kellogg reaction. A single ketone can also be converted to the corresponding alkene via its tosylhydrazone, using
sodium methoxide Sodium methoxide is a Compound (chemistry), chemical compound with the formula CH3ONa. This white solid, which is formed by the deprotonation of methanol, is a widely used reagent in industry and the laboratory. It is also a dangerously caustic ...

sodium methoxide
(the
Bamford–Stevens reactionThe Bamford–Stevens reaction is a chemical reaction whereby treatment of tosylhydrazones with strong base gives alkenes. It is named for the British chemist William Randall Bamford and the Scottish chemist Thomas Stevens Stevens (1900–2000). The ...
) or an alkyllithium (the
Shapiro reaction The Shapiro reaction or tosylhydrazone decomposition is an organic reaction in which a ketone or aldehyde is converted to an alkene through an intermediate hydrazone in the presence of 2 equivalents of organolithium reagent. The reaction was discove ...

Shapiro reaction
).


Synthesis from alkenes: olefin metathesis and hydrovinylation

Rhenium- and molybdenum-containing
heterogeneous catalysis of ethene on a catalytic solid surface (1) Adsorption (2) Reaction (3) Desorption In chemistry, heterogeneous catalysis is catalysis where the Phase (matter), phase of catalysts differs from that of the reactants or product (chemistry), products ...
are used in this process, which is used commercially for the interconversion of ethylene and 2-butene to propylene: :CH2=CH2 + CH3CH=CHCH3 → 2 CH2=CHCH3 Transition metal catalyzed hydrovinylation is another important alkene synthesis process starting from alkene itself. It involves the addition of a hydrogen and a vinyl group (or an alkenyl group) across a double bond.


From alkynes

Reduction of
alkyne In organic chemistry Organic chemistry is a branch of that studies the structure, properties and reactions of s, which contain in .Clayden, J.; Greeves, N. and Warren, S. (2012) ''Organic Chemistry''. Oxford University Press. pp. 1–15. . ...

alkyne
s is a useful method for the
stereoselectiveIn chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo ...
synthesis of disubstituted alkenes. If the ''cis''-alkene is desired,
hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant ...

hydrogenation
in the presence of Lindlar's catalyst (a heterogeneous catalyst that consists of palladium deposited on calcium carbonate and treated with various forms of lead) is commonly used, though hydroboration followed by hydrolysis provides an alternative approach. Reduction of the alkyne by
sodium Sodium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

sodium
metal in liquid
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct ch ...

ammonia
gives the ''trans''-alkene. For the preparation multisubstituted alkenes,
carbometalation A carbometalation is any reaction where a carbon-metal bond reacts with a carbon-carbon π-bond to produce a new carbon-carbon σ-bond and a carbon-metal σ-bond. The resulting carbon-metal bond can undergo further carbometallation reactions (olig ...

carbometalation
of alkynes can give rise to a large variety of alkene derivatives.


Rearrangements and related reactions

Alkenes can be synthesized from other alkenes via
rearrangement reactionA rearrangement reaction is a broad class of organic reactionImage:Claisen Rearrangement Scheme.png, 400px, The Claisen rearrangementOrganic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are ...

rearrangement reaction
s. Besides
olefin metathesis Olefin metathesis is an organic reaction that entails the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon chemical bond, double bonds. Because of the relative simplicity of olefin metathesis, it ...
(described above), many
pericyclic reactionIn organic chemistry, a pericyclic reaction is the type of organic reactionImage:Claisen Rearrangement Scheme.png, 400px, The Claisen rearrangementOrganic reactions are chemical reactions involving organic compounds. The basic organic chemistry reac ...
s can be used such as the
ene reaction The ene reaction (also known as the Alder-ene reaction by its discoverer Kurt Alder in 1943) is a chemical reaction between an alkene with an allylic hydrogen (the ene) and a compound containing a multiple bond (the enophile), in order to form a new ...

ene reaction
and the
Cope rearrangement The Cope rearrangement is an extensively studied organic reaction involving the sigmatropic rearrangement, ,3sigmatropic rearrangement of 1,5-dienes. It was developed by Arthur C. Cope and Elizabeth Hardy (chemist), Elizabeth Hardy. For example, ...

Cope rearrangement
. In the
Diels–Alder reaction In organic chemistry, the Diels–Alder reaction is a chemical reaction between a Conjugated system, conjugated diene and a substituted alkene, commonly termed the Diels–Alder_reaction#The_dienophile, dienophile, to form a substituted cyclohexene ...
, a
cyclohexene Cyclohexene is a hydrocarbon with the formula C6H10. This cycloalkene is a colorless liquid with a sharp smell. It is an intermediate in various industrial processes. Cyclohexene is not very stable upon long term storage with exposure to light and ...

cyclohexene
derivative is prepared from a diene and a reactive or electron-deficient alkene.


IUPAC Nomenclature

Although the nomenclature is not followed widely, according to IUPAC, an alkene is an acyclic hydrocarbon with just one double bond between carbon atoms. Olefins comprise a larger collection of cyclic and acyclic alkenes as well as dienes and polyenes. To form the root of the IUPAC names for straight-chain alkenes, change the ''-an-'' infix of the parent to ''-en-''. For example, CH3-CH3 is the
alkane In , an alkane, or paraffin (a historical that also has ), is an . In other words, an alkane consists of and atoms arranged in a structure in which all the s are . Alkanes have the general chemical formula C''n''H2''n''+2. The alkanes rang ...
''ethANe''. The name of CH2=CH2 is therefore ''ethENe''. For straight-chain alkenes with 4 or more carbon atoms, that name does not completely identify the compound. For those cases, and for branched acyclic alkenes, the following rules apply: # Find the longest carbon chain in the molecule. If that chain does not contain the double bond, name the compound according to the alkane naming rules. Otherwise: # Number the carbons in that chain starting from the end that is closest to the double bond. # Define the location ''k'' of the double bond as being the number of its first carbon. # Name the side groups (other than hydrogen) according to the appropriate rules. # Define the position of each side group as the number of the chain carbon it is attached to. # Write the position and name of each side group. # Write the names of the alkane with the same chain, replacing the "-ane" suffix by "''k''-ene". The position of the double bond is often inserted before the name of the chain (e.g. "2-pentene", rather than before the suffix ("pent-2-ene"). The positions need not be indicated if they are unique. Note that the double bond may imply a different chain numbering than that used for the corresponding alkane: C–– is "2,2-dimethyl pentane", whereas C–= is "3,3-dimethyl 1-pentene". More complex rules apply for polyenes and cycloalkenes.


''Cis''–''trans'' isomerism

If the double bond of an acyclic mono-ene is not the first bond of the chain, the name as constructed above still does not completely identify the compound, because of ''cis''-''trans'' isomerism. Then one must specify whether the two single C–C bonds adjacent to the double bond are on the same side of its plane, or on opposite sides. For monoalkenes, the configuration is often indicated by the prefixes ''cis''- (from
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
"on this side of" or ''trans''- ("across", "on the other side of") before the name, respectively; as in ''cis''-2-pentene or ''trans''-2-butene. More generally, ''cis''-''trans'' isomerism will exist if each of the two carbons of in the double bond has two different atoms or groups attached to it. Accounting for these cases, the IUPAC recommends the more general E-Z notation, instead of the ''cis'' and ''trans'' prefixes. This notation considers the group with highest CIP priority in each of the two carbons. If these two groups are on opposite sides of the double bond's plane, the configuration is labeled ''E'' (from the German language, German ''entgegen'' meaning "opposite"); if they are on the same side, it is labeled ''Z'' (from german ''zusammen'', "together"). This labeling may be taught with mnemonic "''Z'' means 'on ze zame zide'".John E. McMurry (2014):
Organic Chemistry with Biological Applications
'; 3rd edition. 1224 pages.


Groups containing C=C double bonds

IUPAC recognizes two names for hydrocarbon groups containing carbon–carbon double bonds, the vinyl group and the
allyl An allyl group is a substituent with the structural formula H2C=CH−CH2R, where R is the rest of the molecule. It consists of a methylene bridge (−CH2−) attached to a vinyl group (−CH=CH2). The name is derived from the Latin word for garlic, ...

allyl
group.


See also

* Alpha-olefin * Annulene * Aromatic hydrocarbon ("Arene") * Cycloalkene * Dendralene * Diene * Nitroalkene * Polyene * Radialene


Nomenclature links

* Rule A-3. Unsaturated Compounds and Univalent Radical

IUPAC Blue Book. * Rule A-4. Bivalent and Multivalent Radical

IUPAC Blue Book. * Rules A-11.3, A-11.4, A-11.5 Unsaturated monocyclic hydrocarbons and substituent

IUPAC Blue Book. * Rule A-23. Hydrogenated Compounds of Fused Polycyclic Hydrocarbon

IUPAC Blue Book.


References

{{Authority control Alkenes,