Conformational search and dimerization study of average structures of asphaltenes

A conformational search of average structures of asphaltenes containing heteratom and a study of aggregation process were made by the MM/QM method. For the asphaltene A monomer, the minimum energy structure corresponds to the SRR conformation. Results for the asphaltene B monomer were not conclusive because the AM1 and ZINDO methods lead to different results: for the AM1 method, the minimum energy structure corresponds to the SSR monomer while for the ZINDO method the energy minimum corresponds to the SRS monomer. The aggregation process was observed and the ΔE of formation of the aggregates were −58.91 and −45.07 kcal/mol, respectively, for A and B asphaltenes. The more important differences between monomers and dimers were analysed.