13C NMR STUDIES OF COALS AND OIL SHALES

The standard C-13 NMR techniques, including pulse Fourier transform (FT) approaches have not been generally useful for solid sample because of 1) the excessive line broadening due to dipole-dipole interactions between C-13 and H magnetic dipoles, 2) chemical shift anisotropies, and 3) long C-13 spin-lattice relaxation times. All of these problems are eliminated in liquids by the normal tumbling motions occurring randomly in the liquid state.