Instances of Isomerization
Isomerizations in hydrocarbon cracking is usually employed in organic chemistry, where fuels, such as pentane, 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.
"Trans-cis isomerism" is where in certain compounds an interconversion of cis and trans isomers can be observed, for instance, with maleic acid and with azobenzene often by photoisomerization. Another example is the photochemical conversion of the trans isomer to the cis isomer of resveratrol::
Other instances are Aldose-ketose isomerism in biochemistry; isomerizations between conformational isomers, which take place without an actual rearrangement for instance inconversion of two cyclohexane conformations; fluxional molecules which display rapid interconversion of isomers e.g. bullvalene; and "valence isomerization": the isomerization of molecules which involve structural changes resulting only from a relocation of single and double bonds. If a dynamic equilibrium is established between the two isomers it is also referred to as valence tautomerism
The energy difference between two isomers is called "isomerization energy". Isomerizations with low energy difference both experimental and computational (in parentheses) are endothermic trans-cis isomerization of 2-butene with 2.6 (1.2) kcal/mol, cracking of isopentane to n-pentane with 3.6 (4.0) kcal/mol or conversion of trans-2-butene to 1-butene with 2.6 (2.4) kcal/mol.
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