Quantifying dispersion interaction: A study of alkane and alkene dimers

In this study, the interaction pattern and energies of a series of hydrocarbon dimers have been investigated by using a highly reliable quantum chemical method (M06-2X/cc-pVTZ). Saturated and unsaturated hydrocarbons in both cyclic and acyclic forms have been modelled to study their interaction. These dimers are found to involve different types of noncovalent interactions such as π-π (dimer of unsaturated hydrocarbons), CH⋅⋅⋅π (dimer of saturated-unsaturated hydrocarbons) and CH⋅⋅⋅HC (dimer of saturated hydrocarbons). Atoms in molecules analysis provides further insight into the presence of these different noncovalent interactions. Interestingly, the saturated hydrocarbon dimers (A-A) are found to have binding energy strengths comparable with those of the dimers of their unsaturated counterparts (E-E). Strong interactions have been observed between the saturated monomers with the corresponding unsaturated monomers (A-E). The energy decomposition analysis using DFT-SAPT method reveals that both dispersion and electrostatic components play nearly equal roles in modulation of the strength of the hydrocarbon-hydrocarbon interaction.