Isomerisation
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In chemistry, isomerization or isomerisation is the transformation of a molecule into a different isomer [1]. In some molecules and under some conditions, isomerisation occurs spontaneously. Many isomers are equal or roughly equal in bond energy, and so they interconvert relatively freely. When the isomerisation occurs intramolecularly it is considered a rearrangement reaction.
Isomerizations occur in many branches of chemistry.
- Isomerisations in hydrocarbon cracking. This is usually employed in organic chemistry, where fuels, such as pentane a straight-chain isomer is heated in the presence of a platinum catalyst (see image). The resulting mixture of straight- and branched-chain isomers then has to be separated. An industrial process is also the isomerisation of n-butane into isobutane.
- Cis-trans isomerism. In certain compounds a interconversion of cis and trans isomers can be observed, for instance with maleic acid and with azobenzene often by photochemical reactions.
- Aldose-ketose isomerism in biochemistry.
- Isomerisations between conformational isomers. These take place without an actual rearrangement for instance inconversion of two cyclohexane conformations
- Fluxional molecules display rapid interconversion of isomers.
The energy difference between two isomers is called isomerisation energy. Isomerisations with low energy difference both experimental and computational (in parentheses) are endothermic trans-cis isomerisation of 2-butene with 2.6 (1.2) kcal/mole, cracking of isopentane to n-pentane with 3.6 (4.0) kcal/mole or conversion of trans-2-butene to 1-butene with 2.6 (2.4) kcal/mole [2]
[edit] References
- ^ Gold Book definition: Link
- ^ How to Compute Isomerization Energies of Organic Molecules with Quantum Chemical Methods Stefan Grimme, Marc Steinmetz, and Martin Korth J. Org. Chem.; 2007; 72(6) pp 2118 - 2126; (Article) DOI:10.1021/jo062446p
