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In situ NMR Methods in Catalysis
Achemist,facedwiththeproblemofdeterminingthemechanismofachemical reaction, tries to identify a set of reactions that will account for the observed behavior:Ideally,asmallsetofknownreactionsshoulddescribeingreatdetail exactly what takes place at each stage of a chemical transformation. The fact that...
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| Auteurs principaux : | , |
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| Format : | Livre |
| Langue : | anglais |
| Titre complet : | In situ NMR Methods in Catalysis / edited by Joachim Bargon, Lars T. Kuhn. |
| Édition : | 1st ed. 2007. |
| Publié : |
Berlin, Heidelberg :
Springer Berlin Heidelberg
, [20..] Cham : Springer Nature |
| Collection : | Topics in current chemistry (Internet) ; 276 |
| Accès en ligne : |
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| Condition d'utilisation et de reproduction : | Conditions particulières de réutilisation pour les bénéficiaires des licences nationales : https://www.licencesnationales.fr/springer-nature-ebooks-contrat-licence-ln-2017 |
| Contenu : | Homogeneous Catalysis in Ionic Liquids. Transfer of Parahydrogen-Induced Hyperpolarization to Heteronuclei. Investigations in Supercritical Fluids. Continuous Asymmetric Hydrogenation. Exploiting Nuclear Spin Polarization to Investigate Free Radical Reactions via in situ NMR |
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| Documents associés : | Autre format:
In situ NMR methods in catalysis Autre format: In situ NMR Methods in Catalysis Autre format: In situ NMR Methods in Catalysis Autre format: In situ NMR methods in catalysis Autre format: In situ NMR Methods in Catalysis Autre format: In situ NMR Methods in Catalysis Autre format: In situ NMR methods in catalysis |
| Résumé : | Achemist,facedwiththeproblemofdeterminingthemechanismofachemical reaction, tries to identify a set of reactions that will account for the observed behavior:Ideally,asmallsetofknownreactionsshoulddescribeingreatdetail exactly what takes place at each stage of a chemical transformation. The fact that many reactions proceed in a stepwise fashion can most convincingly be demonstrated if intermediate species can be isolated and shown to proceed to the same products under otherwise identical reaction conditions. An - termediate is the reaction product of each of these steps, except for the last onethatformsthe?nalproduct. Someintermediatesarestablecompoundsin theirownright;someothers,however,aresoreactivethattheirisolationisnot possible. Occasionally, evidence for the existence of short-lived intermediates may be obtained, in particular by spectroscopic observation. The latter may - low a direct observation or an indirect inference from unusual phenomena occurring in the reaction products during in situ investigations of their c- responding chemical reactions. In NMR spectroscopy, for example, transient emissionandenhanced absorptionlinesmaybeobserved, andoneisinclined to believe that there is a universal and unambiguous reason for their appe- ance. Thisisnotnecessarilythecase,however,sincethisseeminglyidentical phenomenon may have a strikingly different origin: During free radical re- tions,aphenomenoncalledchemicallyinduced dynamicnuclear polarization (CIDNP) may give rise to virtually the same effect as occasionally observed duringhomogeneous(andpossiblyevenheterogeneous)hydrogenations:The latter phenomenon, called parahydrogen-induced polarization (PHIP), has a completely different physical basis. It was ?rst noticed twenty years later than CIDNP and occurs if there is an imbalance of the two spin isomers of symmetric molecules such as dihydrogen when hydrogenating unsaturated compoundsusingappropriatecatalysts. Thesetwoeffects,ifnotdifferentiated properly, can cause misinterpretations of reaction mechanisms, as occurred initially when their different origins had not yet been understood approp- ately |
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| ISBN : | 978-3-540-71427-9 |
| DOI : | 10.1007/978-3-540-71427-9 |