Interaction topologies of the S⋯O chalcogen bond: the conformational equilibrium of the cyclohexanol⋯SO2 cluster

The conformational landscape of the cyclohexanol⋯SO2 cluster was revealed in the gas phase using chirped-pulsed broadband rotational spectroscopy and quantum chemical calculations. Four isomers stabilized by a dominant S⋯O chalcogen bond and cooperative C–H⋯OS and O–H⋯OS secondary weak hydrogen bonds were observed, with a near-parallel orientation of the SO and O–H bonds. Isomers formed by equatorial-gauche cyclohexanol are more stable than the isomers containing axial cyclohexanol. The multiple conformations of cyclohexanol and the versatile binding properties of SO2, simultaneously operating as nucleophile and electrophile through its π-holes and non-bonding electrons lead to a complex conformational behavior when the cluster is formed. The long (2.64–2.85 Å) attractive S⋯O interaction between SO2 and cyclohexanol is mainly electrostatic and the contribution of charge transfer is obvious, with an NBO analysis suggesting that the strength of the S⋯O interaction is nearly two orders of magnitude larger than the hydrogen bonds. This study provides molecular insights into the structural and energetic characteristics that determine the formation of pre-nucleation clusters between SO2 and a volatile organic compound like cyclohexanol.