Alkanes pentacyclic—

Several groups of hydrocarbon biological markers were identified in the coal extracts by mass spectrometry using selected ion scans. n-Alkanes, pristane, sesquiterpenes, several tricyclic alkanes and pentacyclic triterpanes with molecular weights from 398 to 454 were detected. 

The pentacyclic alkene (172) is photochemically reactive and is readily transformed (0°C, quartz filter, MeCN solution) into the hexacyclic alkane (173) in high yield. The reaction is a conventional [2+2] cycloaddition between the olefinic rr-bond and the cr-bond of the cyclopropane ring. Compound (174) reacts analogously, yielding (175). 

Normal and branched alkanes, benzene-alkylbenzenes, copaene, cadalene, phenols, sesquiterpanes, and pentacyclic triterpanes decrease in relative concentration with the maturity of the coal. 

Cyclic Alkanes. In the cyclic fraction the following polycyclic isoprenoid compounds were identified (4) 27 29 steranes> methyl-C2g sterane> C 7 32 Pentacyclic triterpanes of hopane type (except C ft), anathe bicyclic tetraterpane perhydro-8-caro-tane (Table IIJ. 

Two groups of tetracyclic and pentacyclic alkanes, steranes and hopanes, respectively, are presented schematically in Figures 27 and 28. The analysis of these biomarkers requires the optimal combined techniques of GC and MS, as well as a large memory and fast computers. The application of the GC/MS/C analysis of steranes and hopanes in petroleum geochemistry was extensively studied and reviewed Most of the... 

FIGURE 29, The GC/MS/C analysis of the saturated hydrocarbon fraction of an Israeli crude oil (a) total ion current (TIC) (b) trace of fragment mjz 133.133, typical of open-chain alkanes (c) trace of fragment (mass fragmentogram) m/z 133.133, typical for most tri-, tetra- and pentacyclic terpanes, dominated by the hopanes (d) the m/z 217.196 mass fragmentogram, steranes, and (e) the m/z 218.203 fragmentogram, also steranes Traces b-e are SIM of accurate mass (AM) with RP of 5000... 

Other than rt-alkanes, pristane, phytane, and other isoprenoid alkanes that are present in abundance in unaltered oils and easily recognizable by GC and GC-MS analyses, most of the biomarker components are present in trace amounts. Among these, naphthenic hydrocarbons, including tricyclic terpanes, pentacyclic triterpanes, and steranes, have been studied most extensively because they carry more specific information on source and depositional environment than normal and isoprenoid alkanes [21]. 

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