Conformational properties of cyclooctane: a molecular dynamics simulation study

Atomistic molecular dynamics simulations have been used to elucidate the conformational properties of cyclooctane in the gas and bulk liquid phases. Accurate reproduction of the gas phase structure, and of the liquid phase densities and solubility parameters have been used as prerequisites to the prediction of conformational properties. The gas phase results clearly indicate the presence of a conformational mixture consisting of the crown, boat-chair, twist-boat-chair and boat-boat conformers at all temperatures (161, 313 and 400K) studied. The fraction of the crown family of conformers was found to be relatively insensitive to temperature. However, the relative concentrations of the twist-boat-chair and boat-chair conformations was found to be highly temperature dependent with the boat-chair being favoured at low temperatures. Bulk packing was found to have a profound effect on the conformational properties in the liquid phase. At the temperatures studied(313 and 400K) the boat-chair family was predominant, with the crown and boat families being essentially absent. The twistboatchair conformation was detected in the liquid phase at both temperatures. The pseudorotation pathway for the twist-boat-chair to boat-chair interconversion was prevalent in both gas and liquid phases establishing the conformational flexibility and the relative importance of the twist-boat-chair conformer in comparison to the crown family. The study successfully explains the separate experimental findings in both the gas and liquid phases of cyclooctane.