Abstract
High resolution dipolar/chemical shift NMR experiments for solids are critically reviewed and used to measure
l5N-*H bond distances in a series of compounds, many of which have also been studied by neutron diffraction. The results
demonstrate that when recorded carefully, with attention paid to the experimental procedures described, two-dimensional
dipolar/chemical shift spectra can yield bond distances accurate to within 0.005 Á and mutual orientations of dipolar and
chemical shift tensors accurate to within 3°. A comparison of the NMR distances with similar data from neutron diffraction
experiments shows the NMR distances to be uniformly ~0.035 Á longer, a result that is consistent with some vibrational
averaging of the 15N-'H dipolar interaction. Collectively, the experimental data and procedures described here demonstrate
for the first time that high resolution dipolar/chemical shift NMR experiments are a viable method for locating protons in
polycrystalline or amorphous solids. Previously, such determinations have been possible only with single crystal neutron diffraction
techniques.