13C NMR chemical shift anisotropy for benzene adsorbed on charcoal and silica gel

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Abstract
The 13C NMR chemical shift anisotropy powder patterns under conditions of proton decoupling have been determined for benzene (13C enriched) adsorbed on charcoal and silica gel and for toluene adsorbed on charcoal. These spectra do not differ significantly from those of the pure solid as far as principal values of the chemical shift tensor are concerned. The simultaneous presence of molecules in various states of motional narrowing of the anisotropy powder pattern is revealed, in agreement with earlier observations of dipolar broadened proton spectra for similar systems. Motional narrowing effects observable for the toluene molecule in the adsorbed state aid in the assignment of principal axes.