The "N chemical shift tensors of uracil are reported using I5N powder pattem techniques. The principal values of the I5N uracil tensors are obtained from the spectra of [l-'5N]uracil and [3-'jN]uracil, and the tensor orientations are determined from the spectrum of [ 1,3-'5N2,2-'3C]~ra~i1 by including the effects of the direct dipolar interaction in the spectral fitting routine. Ambiguities in the orientational assignments, which arise from the axial symmetry of the direct dipolar tensor, are resolved using molecular symmetry considerations and results of ab initio calculations of I5N chemical shielding tensors. The NI nitrogen has principal values of 196, 114, and 30 ppm and the N3 nitrogen 200, 131, and 79 ppm with respect to I5NH4N03. Assuming that the smallest (most shielded) chemical shift tensor components are oriented perpendicular to the molecular plane, the largest components are found to lie 18" and 9" off the NI-H and N3-H bonds, respectively, rotated toward CZ and Cq. These orientations are in good agreement with those calculated theoretically. In addition, inclusion of intermolecular hydrogen bond effects in the theoretical calculations significantly improves the correlation between the calculated and experimental principal values.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.