Identification of a Novel Series of Benzohopanes and Their Geochemical Significance

Abstract

A series of novel C33–C35 hexacyclic benzohopanes (C33b-C35b) were identified in 39 samples of coal extracts and 39 crude oils of different ages from all over the world. C33b and C34b homologues were isolated, and their structures were determined by nuclear magnetic resonance. The structure of C35b benzohopane was proposed based on the mass spectrum and its similarity with the mass spectra of structurally defined C33b and C34b homologues. The structures of the C33b-C35b hexacyclic benzohopanes are closely related to isohopanes; both groups are typical for terrestrial organic matter and can be useful in the correlation analysis. A possible pathway of formation of these novel benzohopanes and their hopanoid precursors with an additional branch in the aliphatic side chain is proposed. C33b–C35b hexacyclic benzohopanes are stable up to the maturity level corresponding to random vitrinite reflectance (Rr) of ∼0.80%, which was demonstrated by analyzing the samples of different maturity and by the maturation sim...