Identification of the methylhopanes in sediments and petroleum

Journal Article · Mon Jan 01 04:00:00 EST 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90212-4· OSTI ID:6755561

Summons, R E ^[1]; Jahnke, L L ^[2]

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1. Bureau of Mineral Resources, Canberra (Australia)
2. NASA Ames Research Center, Moffett Field, CA (USA)

Three C{sub 31} methylhopanes have been prepared by partial synthesis from appropriate diplopetrol precursors. 2{alpha}-Methyldiplopterol, 2{beta}-methyldiplopterol, and a mixture of diplopterol and 3{beta}-methyldiplopterol were each converted to the corresponding 17{alpha}(H), 21{beta}(H)-hopane. Comparison of these standards, using gas chromatography-mass spectrometry with multiple reaction monitoring, with the hopanoids from a variety of bitumens showed that all three C{sub 31} hydrocarbons may occur in sediments and that they are members of C{sub 28} and C{sub 30}-C{sub 36} pseudohomologous series. 2{alpha}-Methyl-17{alpha}(H), 21{beta}(H)-hopane, and 3{beta}-methyl-17{alpha}(H), 21{beta}(H)-hopane are most commonly encountered in mature bitumens. 2{beta}-Methyl-17{alpha}(H), 21{beta}(H)-hopane occurs in some immature bitumens, is much less abundant in others of intermediate maturity, and appears to be absent from mature samples. This, and the similarity of the distribution patterns of homohopane and methylhomohopane isomers, indicates that the common sedimentary methylhopanes are probably derived from biogenic precursors via diagenetic processes analogous to those which give rise to hopanes. In the case of the 2{alpha}-methyl series, common to petroleum and mature sediments, derivation from the 2{beta}-methyl hopanoids found in certain bacteria implies a maturity-related change in the configuration at C-2.

• OSTI ID: 6755561
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:1; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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