Gas-Phase Benzene-Methanol Dimer Configurations: Geometries, Relative Stabilities, and Interaction Energies

The benzene···methanol dimer is one of the simplest systems that manifests an O-H···π nonbonded interaction. This interaction can be found in numerous systems, ranging from small-molecule clusters to biological systems, for example, phenyl-containing ligands bound within a protein's binding pocket. Herein, four gas-phase configurations are examined using quantum mechanics, which have O-H···π, CH₃···π and Bz-H···O interactions. Geometry optimization and frequency calculations were performed up to the MP2/aug-cc-pVQZ theory level, with electronic energies obtained up to the CCSD(T)/complete basis set (CBS) limit. Considering the electronic energy (ΔE_el), the O-H···π configuration is the most stable, with a CCSD(T)/CBS (counterpoise corrected) interaction energy of -4.09 kcal mol^-1, while the other three configurations ranged from -2.00 to -2.60 kcal mol^-1. Using scaled harmonic frequencies, the temperature influence was investigated by computing Gibbs relative and interaction free energies over a 10-800 K temperature range.