Molecule of the Month

28,30-Dinorhopane (Bisnorhopane) by Paul Farrimond

Although more correctly referred to as 28,30-dinorhopane, this compound has long been called “bisnorhopane” in petroleum geochemical literature, and both are now in common use. It is an unusual hopanoid lacking the C-28 and C-30 methyl groups, and thus unlikely to be derived from the widespread bacteriohopanepolyol precursor compounds of most hopanoids in oils and source rocks.

Bisnorhopane has a very patchy distribution in oils. In many it is not detectable, whilst in others it can be a very abundant component, notable examples including many North Sea and Monterey oils. Its source has not been identified, but evidence suggests that it probably derives from microbes, possibly bacterial mats on the sea floor, under anoxic conditions. Interestingly, in the source rocks where it is found, bisnorhopane is present in the solvent extract but not the kerogen (Moldowan et al., 1984), indicating that its precursor compound may lack functional groups to bind into the kerogen structure. Consequently, the concentration of bisnorhopane in a source rock falls with increasing maturation due to the generation of other compounds from the kerogen. Nevertheless, it is an extremely useful biomarker for oil-oil and oil-source correlations. More detail on its use as a stratigraphic marker can be found in a Technical Note on IGI’s website (Garner, 2019).

 

References:

Garner L. (2019). The use of 28,30-bisnorhopane as a stratigraphic marker. Technical Note #17 (IGI Website).

Moldowan J.M., Seifert W.K., Arnold E. & Clardy J. (1984). Structure proof and significance of stereoisomeric 28,30-bisnorhopanes in petroleum and petroleum source rocks. Geochimica et Cosmochimica Acta 48, 1651-61.