تماكب

في الكيمياء، التماكب أو التزامر أو الأزمرة (isomerization) هو تحول جزيء أو أيون متعدد الذرات أو شظية جزيئية إلى متزامر (isomer ) ببنية كيميائية مختلفة.^[1] وفى بعض الجزيئيات وتحت ظروف معينة، يحدث التزامر بصورة تلقائية.^[2] Enolization is an example of isomerization, as is tautomerization.^[3] When the isomerization occurs intramolecularly it may be called a rearrangement reaction.

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.^[4]

Formation of decaphenylferrocene from its linkage isomer.PNG

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أمثلة وتطبيقات التزامر

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 of n-butane to i-butane.^{[بحاجة لمصدر]}

{\ce {{\overset {n-butane}{CH3CH2CH2CH3}}-> {\overset {i-butane}{CH3CH(CH3)CH3}}}}

Fuels containing branched hydrocarbons are favored for internal combustion engines for their higher octane rating.^[5]

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.^{[بحاجة لمصدر]}

The trans isomer of resveratrol can be converted to the cis isomer in a photochemical reaction.^[6]

الهامش

^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "isomerization".
^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "isomerization".
^ 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
^ "Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. 2002. doi:10.1002/14356007.a13_227. ISBN 3527306730. {{cite encyclopedia}}: Cite uses deprecated parameter |authors= (help)
^ 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.

المصادر

ويكيبيديا الإنجليزية.

هذه المقالة عبارة عن بذرة تحتاج للنمو والتحسين؛ فساهم في إثرائها بالمشاركة في تحريرها.

هذه بذرة مقالة عن موضوع علمي تحتاج للنمو والتحسين، ساهم في إثرائها بالمشاركة في تحريرها.

هذه بذرة مقالة عن الكيمياء تحتاج للنمو والتحسين، ساهم في إثرائها بالمشاركة في تحريرها.

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

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

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

[4] 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

[5] "Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. 2002. doi:10.1002/14356007.a13_227. ISBN 3527306730. {{cite encyclopedia}}: Cite uses deprecated parameter |authors= (help)

[6] 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.

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