Structural investigations of three triazines: solution-state NMR studies of internal rotation and structural information from solid-state NMR, plus a full structure determination from powder x-ray diffraction in one case

Three model 2,4,6-tris(amino)-1,3, 5-triazines, structurally related to a dyestuff molecule previously studied by NMR, were synthesized in order to enable the effects of rotamer exchange on the NMR spectra to be investigated in more detail. Two of the compounds are novel. Internal rotation of the triazine ring substituents was studied by variable-temperature solution-state H-1, C-13 and N-15 NMR spectroscopy. All the expected rotamers were detected for each molecule. Rotamer exchange rates varied from slow to fast over the temperature range -40 to 90degreesC, as observed for the dyestuff molecule itself. Solid-state C-13 and N-15 NMR provided information about the structures of the solid molecules. A full crystal structure determination from high-resolution powder x-ray diffraction was achieved for one of the molecules using simulated annealing techniques. Ab initio MO and N-15 NMR chemical shift calculations, based on energy-minimized structures derived from the x-ray structure determination, enabled the effect of intermolecular hydrogen bonding on the N-15 NMR chemical shifts to be studied. The results compared favourably with the experimental solid-state N-15 NMR shifts. Copyright (C) 2003 John Wiley Sons, Ltd.