th  - 1988 - 51st ENC Conference

~'-O-i 0 N i0:55
MEASUREMENTS OF TWO-DIMENSIONAL NMR POWDER PATTERNS IN ROTATING
ISOLIDS.T. Nakal, J. Ashida and T. Terao , Department of Chemistry,
Faculty of Science, Kyoto University, Kyoto 606, Japan.
Switching-angle sample-splnnlng techniques for measuring the heteronuclear
dipolar/chemlcal shift 2D powder patterns are reported. The techniques have the
advantages of the high slgnal-to-nolse ratio and the low distortion of the spectrum
compared with those in stationary powder samples. Furthermore, for compounds with
more than one chemically distinct nucleus, the individual 2D powder patterns can be
separately obtained by 3D NMR. Practical applications of these techniques are
demonstrated with the 13C 2D powder patterns of calcium formate, polyethylene, and
polyacetylene. The chemical shift tensors and proton positions in calcium formate
were obtained for the two crystallographlcally inequivalent formate ions, which
agree with the results already reported by single crystal studles of 13C NMR and
neutron diffraction. The chemical shift principal axes in polyethylene were found
to be only approximately along the symmetry directions of the CH 2 group, indicating
a strong perturbation of the electric environment by the crystal field.
Current address: Department of Chemistry, University of California, Berkeley,
"CA 94720.
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