Combined variable-temperature and variable-field ~(15)N cross-polarization magic angle spinning NMR study of ~(15)N, ~(14)N residual dipolar coupling in pyrazole derivatives

摘要

A study of the residual dipolar ~(15)N, ~(14)N coupling observed in ~(15)N cross-polarization magic angle spinning NMR spectra at variable temperature and variable field in 1-amino- and 1-nitropyrazole is reported. Residual dipolar ~(15)N,~(14)N coupling is present in high-resolution ~(15)N spectra as an asymmetric(2:1) doublet induced by the quadrupolar ~(14)N neighbouring nitrogen on the corresponding ~(15)N 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 ~(14)N site, were used to obtain successful splitting values