Conformation of Ethylene Glycol in the Liquid State: Intra- versus Intermolecular Interactions

Ethylene glycol is a typical rotor molecule with the three dihedral angles that allow for a number of possible conformers. The geometry of the molecule in the liquid state brings into sharp focus the competition between intra- and inter-molecular interactions in deciding conformation. Here, we report a conformational analysis of ethylene glycol in the liquid state from ab initio molecular dynamics simulations. Our results highlight the importance of intermolecular hydrogen bonding over intramolecular interactions in the liquid, with the central OCCO linkage adopting both gauche and trans geometries in contrast to the gas phase, wherein only the gauche has been reported. The influence of intermolecular interactions on the conformation of the terminal CCOH moieties is even more striking, with certain regions of conformational space, wherein the ethylene glycol molecule cannot participate with its full complement of intermolecular hydrogen bonds, excluded. The results are in agreement with Raman and NMR spectroscopic studies of liquid ethylene glycol, but at the same time they are able to provide new insights into how intermolecular interactions favor certain conformations while excluding others.