High Internal Energies of Proposed Asphaltene Structures

Molecular structures proposed in the literature as representative of asphaltenes attempt to encompass the results of numerous experiments and quantum mechanics calculations. This work demonstrates that certain features of chemical bonding in proposed structures lead directly to high energies and thus low relative occurrence probabilities. Hartree-Fock, quantum density functional theory, and classical force field calculations indicate features such as nonplanar aromatic rings that occur in structures proposed recently in the literature. Energy differences for altered pendant group locations were compared using smaller molecules as a reference. Small changes to side-chain positions preserve the overall architecture of the proposed asphaltene molecules while decreasing repulsive forces and restoring planar aromatic rings. The resulting structures are more appropriate for pursuing molecular hypotheses about asphaltenes.