Orientations of the 17O electric-field-gradient tensor and chemical shift tensor in benzamide: NMR of dipolar coupled spins

We report a solid-state 17O NMR study of [α-13C,17O] benzamide. The orientations of the 17O electric-field-gradient and chemical shift tensors were determined from analysis of magic-angle spinning and stationary 17O NMR spectra. The largest electric-field-gradient component lies in the amide plane and perpendicular to the 13C–17O dipolar vector, whereas the intermediate electric-field-gradient component is along the CO bond. It is also found that the principal component of the 17O chemical shift tensor with the least shielding, δ11, is approximately 18° off the CO bond and that the component with the most shielding, δ33, is perpendicular to the amide plane. The present study confirms our earlier results of quantum chemical calculations.