Piotr Tekely

Molecular structure of coals: A debate

Abstract Recent evidence concerning the molecular phase present in coals is discussed. It is proposed that pyrolysis-field ionization mass spectrometry (py-f.i.m.s.) provides information on the chemical nature of such material, but caution is also suggested in these interpretations. N.m.r. experiments can give information concerning the spatial location of molecular species, and domains with different mobilities can be recognised. The importance of considering coal origins and petrology in discussions of coal structure is emphasized. An empirical perspective of the molecular phase is afforded by solvent-free catalytic hydrogenation. Coal depolymerization by solvated electrons yields products consistent with polymethylene as a major part of the macromolecular network. The relation of these observations to the molecular mass of extracted material is suggested as crucial.

Observation of 1H nuclei in heterogeneous solids via cross-polarization 13C N.M.R.

The complementary advantages of high sensitivity and high chemical shift dispersion offered by 1H and 13C spins are exploited in experiments designed for indirect observation of the proton system through 13C resonances. Pulse sequences devised for indirect measurements of proton T 2 relaxation times and for indirect observation of proton spin diffusion (an extension of the Goldman-Shen experiment) are presented and compared to direct proton measurements. A proper image of the structural heterogeneity, manifested by three distinct physical regions, is deduced from indirect measurements on static and rotating samples of polyoxymethylene. The results are used as a model for illustrating the potential of the proposed sequences. Possible restrictions on the quantitative analysis of the extent of the different morphological regions are discussed in terms of their different cross-polarization characteristics.