The15 N NMR chemical shifts of N 7 -and N 9 -substituted purine derivatives were investigated systematically at the natural abundance level of the 15 N isotope. The NMR chemical shifts were determined and assigned using GSQMBC, GHMBC, GHMQC and GHSQC experiments in solution.15 N cross-polarization magic angle spinning data were recorded for selected compounds in order to study the principal values of the 15 N chemical shifts. Geometric parameters obtained by using RHF/6-31G * * and single-crystal x-ray structural analysis were used to calculate the chemical-shielding constants (GIAO and IGLO) which were then used to assign the nitrogen resonances observed in the solid-state NMR spectra and to determine the orientation of the principal components of the shift tensors.