Combined variable-temperature and variable-field15N cross-polarization magic angle spinning NMR study of15N,14N residual dipolar coupling in pyrazole derivatives

Abstract

A study of the residual dipolar 15N,14N coupling observed in 15N cross‐polarization magic angle spinning NMR spectra at variable temperature and variable field in 1‐amino‐ and 1‐nitropyrazole is reported. Residual dipolar 15N,14N coupling is present in high‐resolution 15N spectra as an asymmetric (2 : 1) doublet induced by the quadrupolar 14N neighbouring nitrogen on the corresponding 15N signal. The observed spectral splittings were theoretically established by means of a second‐order perturbing treatment of the complete Hamiltonian. X‐ray diffraction and NQR data and theoretical calculations, in conjunction with several assumptions regarding the quadrupole tensor at each 14N site, were used to obtain successful splitting values. Copyright © 2000 John Wiley & Sons, Ltd.