N-15 NMR spectroscopy of cyclotriphosphazenes and polyphosphazenes based on P-31, N-15 HMQC correlations

A P-31 and N-15 NMR Study of cyclotriphosphazenes 1-4 and polyphosphazene 5 has been carried out including solvent and substituent effects. N-15 chemical shifts and P-31, N-15 coupling constants are readily obtained through 1D and 2D P-31, N-15 HMQC correlation spectroscopy on natural-abundance samples. This methodology combined with spectral simulation also yields N-15-induced isotope shifts. P-31 and N-15 are both relatively insensitive to changes in solvent polarity. Chemical shifts are reasonably explained in terms of electronic density variations, and P-31, N-15 couplings are rationalized by considering their absolute sign, which depends on the substituent bonded to phosphorus. N-15 proved to be more sensitive to structural modifications than P-31. Therefore, the availability of N-15 NMR data on cyclotriphosphazenes can be considered a valuable tool in the design of model compounds for polyphosphazene synthesis. (C) 1996 Academic Press, Inc.