Isomerization

In chemistry isomerization or isomerisation is the process in which a molecule, ion or molecular fragment is transformed into an isomer with a different chemical structure.^[1] Enolization is an example of isomerization, as is tautomerization.^[2] When the isomerization occurs intramolecularly it may be called a rearrangement reaction.^{[citation needed]}

When the activation energy 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, $\Delta G^{\circ }$ , have been calculated, with good agreement between observed and calculated data.^[3]

Examples and applications[]

Alkanes[]

Skeletal isomerization occurs in the cracking process, used in the petrochemical 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.^{[citation needed]}

CH_{3}CH_{2}CH_{2}CH_{3}

(n-butane) →

CH_{3}CH(CH_{3})CH_{3}

(i-butane)

Fuels containing branched hydrocarbons are favored for internal combustion engines for their higher octane rating.^[4]

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.^{[citation needed]}

The trans isomer of resveratrol can be converted to the cis isomer in a photochemical reaction.^[5]

Thermal rearrangement of azulene to naphthalene has been observed.^{[citation needed]}

Other examples[]

Aldose-ketose isomerism, aka Lobry de Bruyn–van Ekenstein transformation, provides an example in saccharide chemistry.^{[citation needed]}

An example of an organometallic isomerization is the production of decaphenylferrocene, [(η⁵-C₅Ph₅)₂Fe] from its linkage isomer.^[6]^[7]

References[]

^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "isomerization". doi:10.1351/goldbook.I03295
^ Antonov L (2016). Tautomerism: Concepts and Applications in Science and Technology (1st ed.). Weinheim, Germany: Wiley-VCH. ISBN 978-3-527-33995-2.
^ 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
^ Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer, Hartmut Höke (2002). "Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_227.CS1 maint: uses authors parameter (link)
^ Resveratrol Photoisomerization: An Integrative Guided-Inquiry Experiment Elyse Bernard, Philip Britz-McKibbin, Nicholas Gernigon Vol. 84 No. 7 July 2007 Journal of Chemical Education 1159.
^ Brown, K. N.; Field, L. D.; Lay, P. A.; Lindall, C. M.; Masters, A. F. (1990). "(η⁵-Pentaphenylcyclopentadienyl){1-(η⁶-phenyl)-2,3,4,5-tetraphenylcyclopentadienyl}iron(II), [Fe(η⁵-C₅Ph₅){(η⁶-C₆H₅)C₅Ph₄}], a linkage isomer of decaphenylferrocene". J. Chem. Soc., Chem. Commun. (5): 408–410. doi:10.1039/C39900000408.
^ Field, L. D.; Hambley, T. W.; Humphrey, P. A.; Lindall, C. M.; Gainsford, G. J.; Masters, A. F.; Stpierre, T. G.; Webb, J. (1995). "Decaphenylferrocene". Aust. J. Chem. 48 (4): 851–860. doi:10.1071/CH9950851.

[1] IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "isomerization". doi:10.1351/goldbook.I03295

[2] Antonov L (2016). Tautomerism: Concepts and Applications in Science and Technology (1st ed.). Weinheim, Germany: Wiley-VCH. ISBN 978-3-527-33995-2.

[3] 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

[4] Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer, Hartmut Höke (2002). "Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_227.CS1 maint: uses authors parameter (link)

[5] Resveratrol Photoisomerization: An Integrative Guided-Inquiry Experiment Elyse Bernard, Philip Britz-McKibbin, Nicholas Gernigon Vol. 84 No. 7 July 2007 Journal of Chemical Education 1159.

[6] Brown, K. N.; Field, L. D.; Lay, P. A.; Lindall, C. M.; Masters, A. F. (1990). "(η⁵-Pentaphenylcyclopentadienyl){1-(η⁶-phenyl)-2,3,4,5-tetraphenylcyclopentadienyl}iron(II), [Fe(η⁵-C₅Ph₅){(η⁶-C₆H₅)C₅Ph₄}], a linkage isomer of decaphenylferrocene". J. Chem. Soc., Chem. Commun. (5): 408–410. doi:10.1039/C39900000408.

[7] Field, L. D.; Hambley, T. W.; Humphrey, P. A.; Lindall, C. M.; Gainsford, G. J.; Masters, A. F.; Stpierre, T. G.; Webb, J. (1995). "Decaphenylferrocene". Aust. J. Chem. 48 (4): 851–860. doi:10.1071/CH9950851.

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