The nature of olefins and carboxyl groups in an Australian brown coal resin |
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| Authors: | Michael A Wilson Philip J Collin Anthony M Vassallo Nigel J Russell |
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| Institution: | CSIRO Division of Fossil Fuels, P.O. Box 136, North Ryde, N.S.W. 2113, Australia |
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| Abstract: | The chemical structure of the resin from an Australian soft brown coal (Yallourn) has been investigated by cross-polarization nuclear magnetic resonance spectroscopy with magic angle spinning (13C CP MAS NMR). Some additional solution 1H and 13C data were also obtained. Solid-state experiments were performed with and without a delay period before data acquisition. The resulting free induction decays were Fourier transformed with respect to acquisition time and delay period to produce two-dimensional solid-state spectra. Assignments made from the spectra clearly demonstrate that the gross chemical structure of the Yallourn resin is best described as a polymerized diterpenoid with one axial carboxylic group and two double bonds. One double bond is trisubstituted, the other is monosubstituted. After consideration of various mechanisms for polymerization of diterpenoid units during biogenesis and coalification, it was concluded that polymerization occurs at the C15 carbon atoms in the diterpenoids without cyclization of the methylene units at C8. |
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| Keywords: | solid state NMR fossil resins dipolar dephasing |
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