Ultra-low hydrogen content bowl-shaped polycyclic aromatic hydrocarbons in petroleum

Abstract

In the ultra-high resolution mass spectrometric analysis of processed petroleums (fossil materials), we observed species with ultra-low hydrogen content (e.g. H/C ratio from 0.1 to 0.4). Some of the observed chemical formula (C20-40H10) can be rationalized by the known corannulene-based peri-condensed Polycyclic Aromatic Hydrocarbons (PAHs). Other formulas (such as C20-40H8, C20-40H6 and C20-40H4) cannot be rationalized with any known structures. We proposed highly curved non-planar PAHs involving multiple connected five member aromatic rings. These structures do not obey the isolated pentagon rule (IPR). The stabilities of the proposed structures were evaluated by density functional theory. Strain energies were calculated based on hypothetical isodesmic conversion of planar structures to the curved non-planar structures. Results showed that the strain energies of the proposed structures are lower than that of fullerenes of the same carbon number, confirming stabilities of the non-IPR structures. The low hydrogen content species are likely formed in the thermal and/or catalytic cracking of the petroleums. They are possible intermediate molecules on the path toward the formation of fullerenes (buckyballs) and other nano-carbon materials