Bestimmung der Konformation des Schlüsselintermediats einer enantioselektiven Palladium-katalysierten allylischen Substitution mithilfe dipolarer Restkopplungen

Probing Long-Range Anisotropic Interactions: a General and Sign-Sensitive Strategy to Measure 1 H-1 H Residual Dipolar Couplings as a Key Advance for Organic Structure Determination

Residual dipolar couplings (RDCs) are amongst the most powerful NMR parameters for organic structure elucidation. In order to maximize their effectiveness in increasingly complex cases such as flexible compounds, a maximum of RDCs between nuclei sampling a large distribution of orientations is needed, including sign information. For this, the easily accessible one-bond ¹ H-¹³ C RDCs alone often fall short. Long-range ¹ H-¹ H RDCs are both abundant and typically sample highly complementary orientations, but accessing them in a sign-sensitive way has been severely obstructed due to the overflow of ¹ H-¹ H couplings. Here, we present a generally applicable strategy that allows the measurement of a large number of ¹ H-¹ H RDCs, including their signs, which is based on a combination of an improved PSYCHEDELIC method and a new selective constant-time β-COSY experiment. The potential of ¹ H-¹ H RDCs to better determine molecular alignment and to discriminate between enantiomers and diastereomers is demonstrated.

Direct Experimental Evidence for Halogen-Aryl π Interactions in Solution from Molecular Torsion Balances

We dissected halogen-aryl π interactions experimentally using a bicyclic N-arylimide based molecular torsion balances system, which is based on the influence of the non-bonded interaction on the equilibria between folded and unfolded states. Through comparison of balances modulated by higher halogens with fluorine balances, we determined the magnitude of the halogen-aryl π interactions in our unimolecular systems to be larger than -5.0 kJ mol^-1 , which is comparable with the magnitude estimated in the biomolecular systems. Our study provides direct experimental evidence of halogen-aryl π interactions in solution, which until now have only been revealed in the solid state and evaluated theoretically by quantum-mechanical calculations.

Cross-linked helically chiral poly-(γ-benzyl-L-glutamate) as enantiodiscriminating alignment medium

The best of both worlds: By crosslinking poly-(γ-benzyl-L-glutamate) (PBLG), an alignment medium, which combines the scalability of cross-linked polymer gels (strain-induced-alignment media) with the enantiodiscriminating properties of helically chiral PBLG, was obtained. Spectra of excellent quality and residual dipolar couplings (RDCs) of the perfect size can be obtained for small organic compounds (see scheme; Bn = benzyl).