In
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
, isomerization or isomerisation is the process in which a
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...
,
polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zero. The term molecule may or may no ...
or molecular fragment is transformed into an
isomer with a different
chemical structure
A chemical structure determination includes a chemist's specifying the molecular geometry and, when feasible and necessary, the electronic structure of the target molecule or other solid. Molecular geometry refers to the spatial arrangement of ...
.
Enolization
In organic chemistry, alkenols (shortened to enols) are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond (). The ter ...
is an example of isomerization, as is
tautomer
Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert.
The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hy ...
ization. When the isomerization occurs
intramolecularly it may be called a
rearrangement reaction.
When the
activation energy
In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules p ...
for the isomerization reaction is sufficiently small, both isomers will exist in a temperature-dependent
equilibrium with each other. Many values of the standard
free energy difference,
, have been calculated, with good agreement between observed and calculated data.
Examples and applications
Alkanes
Skeletal isomerization occurs in the
cracking process, used in the
petrochemical
Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewabl ...
industry. As well as reducing the average chain length, straight-chain hydrocarbons are converted to branched isomers in the process, as illustrated the following reaction of
''n''-butane to
''i''-butane.
:
\overset -> \overset
Fuels containing branched
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 ...
s are favored for internal combustion engines for their higher
octane rating.
Alkenes
Terminal alkenes isomerize to internal alkenes in the presence of metal catalysts. This process is employed in the
Shell higher olefin process to convert alpha-olefins to internal olefins, which are subjected to
olefin metathesis. In certain kinds of alkene polymerization reactions,
chain walking is an isomerization process that introduces branches into growing polymers.
The ''trans'' isomer of
resveratrol can be converted to the ''cis'' isomer in a photochemical reaction.
:
Thermal rearrangement of
azulene to
naphthalene
Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromat ...
has been observed.
Other examples
Aldose-ketose isomerism, aka Lobry de Bruyn–van Ekenstein transformation, provides an example in
saccharide chemistry.
:
An example of an
organometallic isomerization is the production of decaphenylferrocene, from its
linkage isomer.
See also
*
Base-promoted epoxide isomerization
*
Epimerization
*
Racemization
*
Tautomerization
Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert.
The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hyd ...
*
Linkage isomerism
In chemistry, linkage isomerism or ambidentate isomerism is a form of isomerism in which certain coordination compounds have the same composition but differ in their metal atom's connectivity to a ligand.
Typical ligands that give rise to linka ...
References
{{Reaction mechanisms
Chemical reactions