Ethylene glycol dimers in the liquid phase: A study by x-ray and neutron diffraction

Molecular conformations and intermolecular H bonding in liquid ethylene glycol have been studied by neutron diffraction with hydrogen/deuterium isotopic substitution, and by x-ray diffraction measurements at room temperature. For comparison, conformations of molecules and their dimers in the gas phase have also been calculated, based on the density-functional theory. Energies, geometries, and vibrational frequencies of dimers were analyzed. Diffraction data analyzed by the Monte Carlo method resulted in a molecular structure in agreement with the findings from gas-phase electron diffraction experiments and density-functional calculations. Conformers of ethylene glycol molecules in the liquid phase were identified as a gauche OCCO arrangement, stabilized by intramolecular hydrogen bonding, which is in agreement with the results of gas-phase density-functional calculations. Data analysis resulted in an average of three hydrogen-bonded nearest neighbors of molecules in liquid ethylene glycol. In addition, experimental composite pair correlation functions RHO and RR have been extracted from the diffraction data for future comparison with computer simulation results.