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

We report a solid-state O-17 NMR study of [alpha-C-13,O-17] benzamide. The orientations of the O-17 electric-field-gradient and chemical shift tensors were determined from analysis of magic-angle spinning and stationary O-17 NMR spectra. The largest electric-field-gradient component lies in the amid e plane and perpendicular to the C-13-O-17 dipolar vector, whereas the inte rmediate electric-field-gradient component is along the C=O bond. It is als o found that the principal component of the O-17 chemical shift tensor with the least shielding, delta (11), is approximately 18 degrees off the C=O b ond and that the component with the most shielding, delta (33), is perpendi cular to the amide plane. The present study confirms our earlier results of quantum chemical calculations. (C) 2001 Elsevier Science B.V. All rights r eserved.