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 (ΔEel), 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.