The nature and fate of natural resins in the geosphere. IX Structure and maturation similarities of soluble and insoluble polylabdanoids isolated from Tertiary Class I resinites

Soluble polylabdanoids were isolated from five Tertiary Class I resinites by sequential extraction and were characterized by C-13 and H-1 NMR spectroscopy and Py-GC-MS. The structure and maturation characteristics of soluble extracts were strikingly similar to those observed for polylabdanoids in the native resinite. Soluble and insoluble materials undergo parallel geotransformation processes similar to those observed previously, including (i) exomethylene and total olefinic carbon depletion, (ii) double bond redistribution as indicated by Sigma C-14/Sigma C-15 pyrolysis product ratios and (iii) A-ring defunctionalization. Resonances at 138 and 127 ppm in C-13 NMR spectra were shown to be those of aromatic and olefinic structures in mature samples, indicating that double bond content had been overestimated in the past. Proton NMR analyses have revealed several structural features previously unobserved, Resonances at 5.3 ppm of mature polymers were assigned to trisubstituted olefins in cyclized/cross-linked polylabdanoids. Further evidence in support of this pathway is derived from C-13 NMR spectra, from which an increase in aliphatic carbon content paralleling the loss of olefinic structures was observed. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.