The Six Isomers of the Cyclohexanol Dimer: A Delicate Test for Dispersion Models.

: The cyclohexanol homodimer is a delicate test model of the role of dispersion forces in intermolecular association. While phenol produces a single dimer, suppression of π interactions and larger conformational flexibility in cyclohexanol results in multiple isomerism, as six competing dimers of the free molecule are observed in a supersonic jet expansion. Rotational spectroscopy reveals accurate structural data, specifically the formation of homo- and heterochiral diasteroisomers and the presence of both equatorial and axial forms in the dimers. Four dispersion-corrected density-functional molecular orbital calculations were tested against the experiment, with B3LYP-D3(BJ) offering good structural reproducibility with an Alrich's triple-ζ basis set. However, the prediction of the dimer energetics is largely model-dependent, offering a testbed for validation of dispersion-corrected computational models.