Experimental determination of orientations for the 17O electric-field-gradient and chemical shielding tensors in l-alanine

We have presented a solid-state 17O NMR study of [13C, 17O]-l-alanine. Using the experimental results for the 13C-17O dipolar vector and Euler angles, the absolute orientations of 17O chemical shielding (CS) and electric-field-gradient (EFG) tensors with respect to the molecular frame can be determined for l-alanine. The present results suggest that the intermediate EFG tensor components, VYY, lie in the carboxylate plane and parallel to the C-O bond directions, while the least shielded components, δ11, and the intermediate CS tensor components, δ22, roughly lie in the molecular plane and the direction of δ22 components are approximately 38° and 25° off the C-O bonds for O1 and O2, respectively. These results are in reasonable agreement with those of our quantum chemical calculations reported previously.