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Degradation of 5 alpha-cholestane into dimethylperhydrophenanthrenes: an experimental and theoretical study

Lookup NU author(s): Mark Sugden, Dr Geoffrey AbbottORCiD


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A tetradeuteriated cholestane was heated with kerogen isolated from the Messel oil shale at 350 degreesC for 25 different time periods (ranging from 0.5 to 80 h) in borosilicate vessels. Three isomers of tetradeuteriated dimethylperhydrophenanthrene were formed and one of these was the major saturated hydrocarbon product under most conditions. The stereochemistry for these isomers was unknown but if the stable 5alpha,8beta,9alpha(H),10beta(CH3) sterane configuration is inherited from the cholestane then there are four possible isomers namely: I and II [13beta(H) and 13alpha(H) diastereomers, respectively, of 10,13-dimethylperhydrophenanthrene] as well as III and IV [14beta(H) and 14alpha(H) diastereomers, respectively, of 10,14-dimethylperhydrophenanthrene]. Molecular mechanics revealed that I is the most stable form and therefore is the component that dominated the saturated hydrocarbon degradation products. The identification of only three isomers of deuteriated dimethylperhydrophenanthrene in the pyrolysis experiments is supported by the calculated stabilities (DeltaDeltaG) as isomer IV is considerably more unstable (by 1.7 kcal/mol) than II which is the least stable of I, II and III. If these compounds can be detected in crude oils their distributions may be useful maturity indicators in oils that have been generated at high thermal maturity. (C) 2004 Elsevier Ltd. All rights reserved.

Publication metadata

Author(s): Sugden MA, van Duin ACT, Abbott GD

Publication type: Article

Publication status: Published

Journal: Organic Geochemistry

Year: 2004

Volume: 35

Issue: 11-12

Pages: 1337-1341

ISSN (print): 0146-6380

ISSN (electronic): 1873-5290


DOI: 10.1016/j.orggeochem.2004.05.003

Notes: Proceedings of the 21st International Meeting on Organic Geochemistry


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