A 3D separated-local-field (SLF) experiment based on the 2D to a spinning sample in a MAS experiment (6) where the PHORMAT technique is described. In the 3D experiment, the spectral overlap caused by the chemical-shift anisotropy inconventional 2D SLF powder pattern for each chemically inequivteraction (CSA) is eliminated at a sample spinning rate alent carbon is separated according to their different isotropic larger than the width of the CSA. However, the high resoluchemical shifts. The dipolar coupling constant of a C-H pair, tion achieved by MAS comes at the expense of information hence the bond distance, and the relative orientation of the chemion the shift tensor.
cal-shift tensor to the C-H vector can all be determined for the
Ideally, one would like a 3D experiment in which the SLF protonated carbons with a single measurement. As the sample pattern for each carbon is isolated by its isotropic shift. Such turns at only about 30 Hz in a MAT experiment, the SLF patterns a 3D SLF experiment is possible by employing the MAT obtained approach those of a stationary sample, and an accuracy experiment (7-9). It has been demonstrated in an initial in the measurement similar to that obtained on a stationary sample is expected. The technique is demonstrated on 2,6-dimethoxynaph-report (10) that the SLF powder pattern for complex molecuthalene, where the 13 C-1 H separated-local-field powder patterns lar structures may be obtained with a 3D PHORMAT experifor the six chemically inequivalent carbons are clearly identified ment to which a dipolar evolution dimension is introduced and measured. The observed dipolar coupling for the methoxy in the third dimension. Originally, homonuclear dipolar decarbon is effectively reduced by the fast rotation of the group about coupling during the dipolar evolution period was not used, its C 3 symmetry axis. The average angle between the C-H bond though better results can be obtained with homonuclear dipodirection and the C 3 rotation axis in the OCH 3 group is found to lar decoupling during the dipolar evolution period. Such a be about 66ะ.