Terpanes pentacyclic

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]. 

There are two observations to be made here. The relative concentration of the sesquiterpanes to the pentacyclic diterpanes decreases with the maturity of the coal. The relative concentration of total terpane to aromatics also decreases with the maturity of the coals. 

Often the higher plant derived terpanes are found in association with their aromatic counterparts. For example, among the aromatic diterpenoids that can dominate the methylated phenanthrenes of bitumens from humic coals are retene, formed from abietoids and phyl-locladoids (Fig. 5.18), and pimanthrene from pimaroids (Fig. 5.30). Similarly, diagnostic pentacyclic aromatic hydrocarbons may be present in ancient sediments and oils, such as 1,2,9-trimethylpicene (derived from 0C-amyrin Fig. 5.22) and 1,8-dimethylpicene (derived from (3-amyrin Fig. 5.30). Abundant 1,2,7-trimethyl-naphthalene relative to other trimethylnaphthalenes... 

FIGURE 28. Structure and numerical assignment of hopanes (pentacyclic C35 terpanes). Compound I (tetrahydroxybacteriohopane), THBH is suggested as the precursor of all hopanes in the geoenvironment. Compounds II represent structures of the derived hopanes (see also Table 5 below)... 

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... 

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