Structural characterization and mass spectrometry fragmentation signatures of macrocyclic alkanes isolated from a Sydney Basin torbanite, Australia

Individual hydrocarbons identified to be macrocyclic alkanes in a torbanite from the Sydney Basin (Australia) were successfully isolated from its extracts using preparative gas chromatography and analyzed by NMR. Saturated cyclic structures were confirmed by single peaks in the NMR 1 H and 13 C spectra indicating single forms of H and C atoms exist in these biomarker molecules. This is consistent with the methylene unit in a ring system assignment of the macrocyclic alkanes and accounts for a formula of (CH 2 ) n . The unusual molecular structures of these compounds are consistent with those that were identified from previous GC retention index data and co-injection with a standard supports the previous research. The mass spectral fragmentation behaviors of representative cyclic alkanes were further investigated by comparing them with the mass spectra of isolated individual macrocyclic alkanes. The characteristic fragment ions in the macrocyclic alkanes of (M–28) + and base peaks of m / z 97, 111, 125, etc., can be assigned as being generated by simple α-/i-cleavage and hydrogen rearrangement. These fragmentation pathways combined with retention indices should assist in differentiating these compounds from monounsaturated alkenes and alkylated monocyclics having similar mass spectral characteristics in other geological samples.