Structural resolution in the carbon-13 nuclear magnetic resonance spectrometric analysis of coal by cross polarization and magic-angle spinning

The origin of the line widths and the prospects for improved structural resolution in /sup 13/C CP/MAS spectra of coal are addressed. Hole-burning and two-dimensional Fourier transformation experiments indicate that inhomogeneous broadening influences are the largest contributors to the /sup 13/C line widths in the spectrum of Powhatan No. 5 coal. This conclusion is confirmed by T/sub 2/ measurements, which indicate homogeneous line widths in the range 2.5-3.5 ppm. The widths of the 'aromatic' and 'aliphatic' bands are therefore attributed mainly to distributions of similar structures and chemical shifts. Double experimental multiplication and convolution difference methods have been found useful in bringing out additional fine structure in the spectra, features that can reasonably be assigned to specific structural moieties. Differential relaxation behaviour shows considerable promise in distinguishing structural differences in the time domain that would not be apparent in the normal /sup 13/C CP/MAS spectrum. However, higher spectrometer sensitivities will be required before this potential can be realized fully.