Proton and 13C solution‐state spectra were obtained for a substituted triazine and assignments made for the signals using different solvents. Site‐exchange effects were observed in 1H spectra at different temperatures below ambient for a CD3OD solution. The bandshapes were fitted for three‐site exchange and the relevant rate constants extracted. The exchange was attributed to internal rotation of the substituents about the triazine ring. Activation parameters were calculated: for exchange between one pair of sites Δ H‡ = 71 ± 4 kJ mol−1 and Δ S‡ = 33 ± 15 J mol−1 K−1, and for a second pair Δ H‡ = 72 ± 5 kJ mol−1 and Δ S‡ = 39 ± 26 J mol−1 K−1, whereas direct exchange between the remaining pair of sites is negligible. Exchange involving a fourth rotamer affects the spectra at lower temperatures, which assists in a partial assignment of the observed peaks to the rotamers. These results are discussed in relation to molecular modelling information and literature values. Solution‐state and solid‐state 13C spectra were also recorded but the latter are broad, making detailed assignment difficult. Copyright © 2000 John Wiley & Sons, Ltd.

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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 1 H, 13 C and 15 N 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 90• C, as observed for the dyestuff molecule itself. Solid-state 13 C and 15 N 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 15 N NMR chemical shift calculations, based on energyminimized structures derived from the x-ray structure determination, enabled the effect of intermolecular hydrogen bonding on the 15 N NMR chemical shifts to be studied. The results compared favourably with the experimental solid-state 15 N NMR shifts.