Molecular Structure of Butanediol Isomers in Gas and Liquid States: Combination of DFT Calculations and Infrared Spectroscopy Studies

Abstract

Density functional theory (Becke3LYP/6-311++G**) conformational analysis was carried out for all positional butanediol isomers. Taking into account the relative populations of the most stable conformers at 298.15 K, the weighted mean enthalpies of each butanediol isomer in the gas state were computed. Combining these results with the experimental values for the enthalpies of vaporization at 298.15 K, an estimate of the enthalpy of each of the butanediol isomers in the liquid state was obtained and discussed. The insight into the structural changes at the molecular level from the isolated molecule to the condensed state was improved by an infrared spectroscopy study in the OH stretching region, which was carried out for a wide range of concentrations of carbon tetrachloride solutions and pure liquids. The spectroscopic studies essentially confirmed the results derived from the combination of the computational and calorimetric studies.