Logically, it should then be "dipterpanes" but only "dipterpenes" gives Google hits.

Actually, Proz' rules recommend one question per entry. You have three here. I think I can help you out with two.

terpanes/steranes/ (dipterpanos?)

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Esteranos y terpanos como marcadores biológicos en la prospección petrolera ...... Mottern, H. H.; Hills, C. H. Ind. Eng. Chem, 1946, 38, 1153- ...

http://en.wikipedia.org/wiki/Sterane
Steranes are a class of 4-cyclic compounds derived from steroids or sterols via diagenetic and catagenetic degradation and saturation. Steranes have an androstane skeleton with a side chain at carbon C-17. The sterane structure constitutes the core of all sterols. Steranes are sometimes used as biomarkers for the presence of eukaryotic cells. [1]

[PDF] The distribution of biomarkers and the geological significance of ...
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http://ingenierosdeminas.org/docu/documentos/biomarcadores_p...

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Note added at 13 hrs (2011-07-15 15:17:55 GMT)
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The last term is "diterpanes":

The Biomarker Guide: Biomarkers and isotopes in petroleum systems ... - Google Books Result
books.google.com.jm/books?isbn=0521837626...
Kenneth E. Peters, Clifford C. Walters, J. Michael Moldowan - 2005 - Science - 1155 pages
Therefore, the seemingly more complex tetracyclic diterpanes that lie near the ... tend to dominate over tricyclic diterpanes in Devonian and Carboniferous ...
Oil shale - Google Books Result
books.google.com.jm/books?isbn=0444414088...
Teh Fu Yen, George V. Chilingar - 1976 - Nature - 292 pages
Possible maturation route of a C20 labdane to give tricyclic diterpanes. It appears that not one of the naturally- occurring tricyclic diterpanes has the ...
[PPT] Présentation PowerPoint
web.mac.com/yannhautevelle/Presentation.../hautevelle-IMOG2.pptFile Format: Microsoft Powerpoint - View as HTML
bi-, tricyclic diterpanes (labdanes, norabietanes, pimaranes, …) ... tetracyclic diterpanes (phyllocladanes, kauranes, beyeranes, …) O/ Coniferales ...

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Note added at 13 hrs (2011-07-15 15:21:55 GMT)
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The Biomarker Guide: Biomarkers and isotopes in petroleum systems ... - Google Books Result
www.books.google.com.jm/books?isbn=0521837626...
"diterpanes"