Solvent independence of structural parameters of furan and thiophene in some liquid crystalline solvents

Furan and thiophene were used as probe molecules to study the solvent effects of liquid crystal (LC) solvents on the NMR determination of molecular structural parameters. It is shown that solvent effects in weakly aligned lyotropic liquid crystalline solvents and some thermotropic LCs are negligible, and the determined structural parameters are in good agreement with expected values. The rα-structures of furan and thiophene were determined in different weak aligned lyotropic liquid crystalline systems and were found to be consistent with each other and with known values within experimental error. The solvent independence of the structural parameters measured in these systems makes them quite promising for structural NMR spectroscopy and allows the determination of the unambiguous NMR structures. Significant solvent effects on the measured structural parameters exist mainly in thermotropic LCs that have large positive diamagnetic anisotropies Δχ and positive sign of DCH of methane, and these effects depend on the order parameters of the target molecules.