Solid state 13C-NMR spectroscopy of some oligocene coals of Assam and Nagaland

Five representative sub-bituminous coals from NE part of India have been analyzed with respect to their distribution of carbon functional groups through C-13 solid state NMR experiments. The C-13 Cross Polarised/Magic Angle Spinning NMR spectra of the coal samples were recorded at temperatures of 23A degrees C, 50A degrees C and 70A degrees C respectively and the changes on their structures were interpreted. The NMR spectra of low rank coals were found to exhibit varying degrees of fine structures. The aromaticities of the coal were also determined from the C/H ratios of coal. Some changes in the peak positions along with the formation of simple aromatic units were observed on mild heating.