Isomerization reaction

In chemistry isomerization (also isomerisation) is the process by which one molecule is transformed into another molecule which has exactly the same atoms, but the atoms have a different arrangement e.g. A-B-C → B-A-C (these related molecules are known as isomers ). In some molecules and under some conditions, isomerization occurs spontaneously. Many isomers are roughly equal in bond energy, and so exist in roughly equal amounts, provided that they can interconvert somewhat freely; that is, the energy barrier between the two isomers is not too high. When the isomerization occurs intramolecularly it is considered a rearrangement reaction.

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.

Isomerization in hydrocarbon cracking is usually employed in organic chemistry, where fuels, such as diesel or pentane, a straight-chain isomer, are heated in the presence of a platinum catalyst. The straight- and branched-chain isomers in the resulting mixture then have to be separated. Another industrial process is the isomerisation of n-butane into isobutane.

Terminal alkenes isomerize to internal alkenes in the presence metal catalysts. This process is employed in the Shell higher olefin process to convert unwanted 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.

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