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Isomerisation

 
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Isomerisation
 
 
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In chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 isomerisation is the process by which one molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 is transformed into another molecule which has exactly the same atoms, but the atoms are rearranged e.g. A-B-C ? B-A-C (these related molecules are known as isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
s ). In some molecules and under some conditions, isomerisation occurs spontaneously. Many isomers are equal or roughly equal in bond energy
Bond energy

In chemistry, bond energy is a measure of bond strength in a chemical bond. For example the carbon-hydrogen bond energy in methane E is the enthalpy change involved with breaking up one molecule of methane into a carbon atom and 4 hydrogen Radical s divided by 4....
, and so exist in roughly equal amounts, provided that they can interconvert relatively freely, that is the energy barrier between the two isomers is not too high.






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In chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 isomerisation is the process by which one molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
 is transformed into another molecule which has exactly the same atoms, but the atoms are rearranged e.g. A-B-C ? B-A-C (these related molecules are known as isomer
Isomer

In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
s ). In some molecules and under some conditions, isomerisation occurs spontaneously. Many isomers are equal or roughly equal in bond energy
Bond energy

In chemistry, bond energy is a measure of bond strength in a chemical bond. For example the carbon-hydrogen bond energy in methane E is the enthalpy change involved with breaking up one molecule of methane into a carbon atom and 4 hydrogen Radical s divided by 4....
, and so exist in roughly equal amounts, provided that they can interconvert relatively freely, that is the energy barrier between the two isomers is not too high. When the isomerisation occurs intramolecularly
Intramolecular

Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule; a property or phenomenon limited to the extent of a single molecule....
 it is considered a rearrangement reaction
Rearrangement reaction

A rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule ....
.

Instances of Isomerization

  • Isomerisations in hydrocarbon cracking
    Cracking (chemistry)

    In petroleum geology and chemistry, cracking is the process whereby complex organic compound molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules by the breaking of carbon-carbon chemical bond in the precursors....
    . This is usually employed in organic chemistry
    Organic chemistry

    Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
    , where fuels, such as pentane
    Pentane

    Pentane is any or one of the organic compounds with the chemical formula C5H12. This alkane is a component of some fuels and is employed as a specialty solvent in the laboratory....
    , a straight-chain isomer, are heated in the presence of a platinum catalyst. The resulting mixture of straight- and branched-chain isomers then have to be separated. An industrial process is also the isomerisation of n-butane into isobutane
    Isobutane

    Isobutane, also known as methylpropane or 2-methylpropane, is an alkane, isomeric with butane. Recent concerns with depletion of the ozone layer by freon gases have led to increased use of isobutane as a gas for refrigeration systems, especially in domestic refrigerators and freezers, and as a propellant in aerosol sprays....
    .
* Trans-cis isomerism. In certain compounds an interconversion of cis and trans isomers
Geometric isomerism

In chemistry, cis-trans isomerism or geometric isomerism or configuration isomerism or E-Z isomerism is a form of stereoisomerism describing the orientation of functional groups within a molecule....
 can be observed, for instance, with maleic acid
Maleic acid

Maleic acid or -butenedioic acid or cis-butenedioic acid or malenic acid or maleinic acid or toxilic acid is an organic compound that is a dicarboxylic acid ....
 and with azobenzene
Azobenzene

Azobenzene is a chemical compound composed of two phenyl rings linked by a azo compound double bond. The term 'azobenzene' or simply 'azo' is often used to refer to a wide class of molecules that share the core azobenzene structure, with different chemical functional groups extending from the phenyl rings....
 often by photoisomerization
Photoisomerization

In chemistry, photoisomerization is molecule behavior in which structural change between isomers is caused by photoexcitation. Both reversible and irreversible photoisomerization reactions exist....
. An example is the photochemical conversion of the trans isomer to the cis isomer of resveratrol
Resveratrol

Resveratrol is a phytoalexin produced naturally by several plants when under attack by pathogens such as bacteria or fungi. Resveratrol has also been produced by chemical synthesis and is sold as a nutritional supplement derived primarily from Japanese knotweed....
 :


  • Aldose-ketose isomerism in biochemistry.
  • Isomerisations between conformational isomers. These take place without an actual rearrangement for instance inconversion of two cyclohexane conformation
    Cyclohexane conformation

    Cyclohexane conformation is a much studied topic in organic chemistry because of the complex interrelationship between the different conformational isomerisms of cyclohexane and its derivatives....
    s
  • Fluxional molecules display rapid interconversion of isomers e.g. Bullvalene
    Bullvalene

    Bullvalene is a hydrocarbon with the chemical formula C10H10 with the unusual property that the chemical bonds making up the molecule are constantly rearranging as in fluxional molecules....
    .


The energy difference between two isomers is called isomerisation energy. Isomerisations with low energy difference both experimental and computational (in parentheses) are endothermic
Endothermic

In thermodynamics, the word endothermic "within-heating" describes a process or reaction that absorbs energy in the form of heat. Its etymology stems from the Greek prefix endo-, meaning ?inside? and the Greek suffix ?thermic, meaning ?to heat?....
 trans-cis isomerisation of 2-butene
2-Butene

2-Butene is a Compound with formula C4H8. It is one of the isomers of butene....
 with 2.6 (1.2) kcal
Calorie

The calorie is a pre-SI metric system unit of energy. The unit was first defined by Professor Nicolas Cl?ment in 1824 as a unit of heat. This definition entered French and English dictionaries between 1841 and 1867....
/mol
Mole (unit)

The mole is a Units of measurement of amount of substance: it is an SI base unit, and one of the few units used to measure this physical quantity....
, cracking of isopentane
Isopentane

Isopentane, carbonhydrogen, also called methylbutane or 2-methylbutane, is a branched-chain alkane with five carbon atoms. Isopentane is an extremely Volatility and extremely flammable liquid at room temperature and pressure....
 to n-pentane with 3.6 (4.0) kcal/mol or conversion of trans-2-butene
Trans-2-butene

Trans-2-Butene is a Compound with formula C4H8.Also see butene....
 to 1-butene
1-Butene

1-Butene is a organic Compound and one of the Isomer of butene. The formula is C4H8....
 with 2.6 (2.4) kcal/mol.