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 b y sequential extraction and were characterized by C-13 and H-1 NMR spectros copy and Py-GC-MS. The structure and maturation characteristics of soluble extracts were strikingly similar to those observed for polylabdanoids in th e native resinite. Soluble and insoluble materials undergo parallel geotran sformation processes similar to those observed previously, including (i) ex omethylene and total olefinic carbon depletion, (ii) double bond redistribu tion as indicated by Sigma C-14/Sigma C-15 pyrolysis product ratios and (ii i) A-ring defunctionalization. Resonances at 138 and 127 ppm in C-13 NMR sp ectra 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 previou sly unobserved, Resonances at 5.3 ppm of mature polymers were assigned to t risubstituted olefins in cyclized/cross-linked polylabdanoids. Further evid ence in support of this pathway is derived from C-13 NMR spectra, from whic h an increase in aliphatic carbon content paralleling the loss of olefinic structures was observed. (C) 1999 Published by Elsevier Science Ltd. All ri ghts reserved.