Mots-clé
(Anglais)
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Raman optical activity (ROA); absolute configuration; solution conformation; solute-solvent interaction; hydrogen bonding; visualisation of ROA generation; atomic contribution pattern; group coupling matrices
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Programme de recherche
(Anglais)
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COST-Action D26 - Integrative Computational Chemistry
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Description succincte
(Anglais)
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Raman optical activity (ROA) is one of the most potent methods for determining the absolute configuration, and the solution conformations, of chiral molecules. Except in empirical comparisons, the precondition for its applicability has so far been that data measured for liquid samples can be meaningfully compared with ab initio computed gas phase data. This condition is satisfied where internal local field corrections suffice. It is violated where specific interactions between solute and solvent molecules exist, such as hydrogen bonding. For plain Raman, observed discrepancies are often of a quantative nature. For ROA they tend to be qualitative ones, with wrong computed signs pointing to wrong absolute configurations. We propose to further the understanding, which at present is marginal, of the influence of specific molecular interactions on observed ROA signs by the use of our powerful graphical methods for visualizing Raman and ROA generation in polyatomic systems. An important tool will be the comparison of the Raman and ROA atomic contribution pattern, and of group coupling matrices, calculated with our highly efficient, rarefied basis sets for isolated molecules on the one hand, and for small clusters of interacting molecules on the other.
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Partenaires et organisations internationales
(Anglais)
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AT, BE, BG, HR, FI, MK, FR, DE, EL, HU, IL, IT, LT, NL, NO, PL, SK, ES, SE, CH, UK
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Résumé des résultats (Abstract)
(Anglais)
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Vibrational spectra reflect the interaction between molecules in the liquid phase. Raman spectroscopy, and Raman optical activity (ROA), are powerful tools for studying such interactions. The successful use of these spectroscopic methods requires the understanding of the differences one observes between the spectra of single molecules, and of the clusters of molecules characteristic of the liquid phase. We have developed a unique procedure for decomposing the vibrational spectra of clusters of molecules into those of the molecules which compose the clusters. The vibrational motions of the nuclei of a cluster are decomposed into the vibrational, rotational, and translational motions of the individual molecules. The relevant electronic tensors are similarly decomposed. An elaborate program implementing much of the theoretical development has been made available to the scientific community under the general public license (GPL). Parts not yet available are currently being coded. The method has been applied to the understanding of the Raman and RAO spectra of hydrogen bonded dimers of chiral carboxylic acids. The unexpected, and spectacular, solvent dependence of the Raman and ROA spectra of 1,4-dimethylenespiropentane, a pure chiral hydrocarbon compound without internal degrees of freedom, has also been studied.
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Références bases de données
(Anglais)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C03.0058
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