Analysis of enantiotopic discrimination in the NMR spectra of prochiral solutes in chiral liquid crystals by symmetry factorization of the Saupe ordering matrix - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Chemical Physics Année : 2009

Analysis of enantiotopic discrimination in the NMR spectra of prochiral solutes in chiral liquid crystals by symmetry factorization of the Saupe ordering matrix

Résumé

The enantiotopic discrimination in the NMR spectrum of prochiral molecules dissolved in chiral liquid crystals CLCs is governed by the ordering of the solute molecules. The lifting of the spectral degeneracy of enantiotopic sites in such solvents stems from the nonequivalence in their effective ordering. This, in turn, is brought about by a change in the directions or the equivalence of the principal axes of their ordering tensor, relative to those in achiral liquid crystals. This discrimination mechanism can only occur for solute molecules belonging to a limited number of “allowed” improper point groups, viz., D2d, C2v, Cs, and S4 (D. Merlet, J. W. Emsley, P. Lesot, and J. Courtieu, J. Chem. Phys. 111, 6890 1999). In this work it is shown that the ordering tensor of such prochiral solutes in CLC, SCLC, and likewise, the tensors, Tk, describing the anisotropic magnetic resonance interactions of enantiotopic pairs, can be partitioned into symmetric and antisymmetric and irrelevant parts. The NMR results in such solvents can be cast into separate sets of equations depending on either the symmetric or the antisymmetric parts of S(CLC) and Tk. The discrimination observed in such solvents depends only on the latter set of equation, while the former applies to the average splitting of enantiotopic pairs as well as to diastereotopic or homotopic sites in the prochiral molecules. The factorization procedure greatly facilitates the analysis of the ordering properties of prochiral solutes in CLC and provides new insight on the discrimination mechanism. In particular, it allows correlation between independent enantiotopic partners and the identification of NMR signals belonging to common prosterogenic faces in the molecule. Expressions relating NMR observables with the symmetric and antisymmetric parts of S(CLC) are derived for each of the four allowed groups. Model examples are presented and discussed.
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Dates et versions

hal-02310983 , version 1 (10-10-2019)

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Philippe Lesot, Christie Aroulanda, Zeev Luz. Analysis of enantiotopic discrimination in the NMR spectra of prochiral solutes in chiral liquid crystals by symmetry factorization of the Saupe ordering matrix. Journal of Chemical Physics, 2009, 131 (10), pp.104501. ⟨10.1063/1.3197853⟩. ⟨hal-02310983⟩
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