Oriented molecules

The natural abundance deuterium 2D Q-COSY NMR spectra of two apolar bridged ring systems, norbornene (C s symmetry) and quadricyclane (C 2 v symmetry), oriented in a chiral liquid crystal made of an organic solution of poly-γ-benzyl-l-glutamate (PBLG), are analyzed. In such a chiral oriented solvent, enantiotopic nuclei or directions are nonequivalent. Consequently, it is possible to measure many more anisotropic interactions compared to those obtained from NMR spectra in nonchiral nematic solvents. From the measurement of all residual quadrupolar splittings, ΔνQ, and one-bond carbon−proton residual dipolar couplings, 1 D C - H, all the elements of the second rank order tensor, S αβ, were calculated. Knowledge of the S αβ values allows all deuterons and subsequently proton NMR resonances to be assigned unambiguously. The reason is that there exists a one-to-one mathematical relationship linking the orientational order parameters of a solute molecule, the molecular geometry, and the anisotropic interactions measured on oriented spectra. In the case of norbornene, it was possible to assign nuclei to each enantiotopic face in this prochiral molecule. Such an analytical approach yields original stereochemical information probing the diastereotopicity and/or enantiotopicity of molecules, and is revealed to be a very useful alternative to conventional 2D-NMR experiments in isotropic solvents.

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Oriented molecules

Cited by 2 publications

References 241 publications

ChemInform Abstract: Oriented Molecules

ChemInform Abstract: Oriented Molecules

Structural Ambiguities Revisited in Two Bridged Ring Systems Exhibiting Enantiotopic Elements, Using Natural Abundance Deuterium NMR in Chiral Liquid Crystals

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