Aufgrund von IR‐, massen‐ und NMR‐spektroskopischen Untersuchungen und Vergleichen werden die drei Haupt‐Sesquiterpen‐Komponenten, die aus dem Petrol‐ äther‐Extrakt von Homogyne alpina(L.)Cass.
Quantum chemical calculations were applied to ethylene sulphite regarded as a model for the structures of 2',3'-cyclic sulphites of nucleosides. The structure of epimeric 2',3'-cyclic sulphites was investigated by spectroscopic methods including 1H-NMR, 1H-NMR with benzene-induced shifts and 13C-NMR. Five-membered cyclic sulphites are configurationally stable (barrier to inversion 180 kJ mol-1). The most stable conformation of the five-membered ring is represented by a twister envelope. According to 1H- and 13C-NMR measurements S configuration was assigned to those epimers of 5'-chloro-5'-deoxy-2',3'-sulphinyluridine and 5'-chloro-5'-deoxy-2',3'-sulphinyl-6-azauridine, which exhibit positive optical rotation. The both epimeric sulphites differ in the position and integral intensity of bands related to stretching vibrations of the S=O group. The epimer, which is more conformationally flexible (S configuration), is preferentially formed.
Several 3,5-methyl substituted fuchsones have been synthesized and characterized by means of UV and NMR spectroscopy as well as dipole moment measurements. Two basic types of behaviour of the longest wavelength band have been found for these derivatives in comparison to 2,6-substituted analogues i.e. hypochromic effect and bathochromic shift. These effects can be attributed to a steric crowding of the C(4)-C(7) double bonds. The role of the steric interactions in the ground state and in the excited state is discussed.
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