Investigation of cross-association behavior in water-ethanol solutions: A combined computational-ATR spectroscopy...

The water/ethanol system possesses complexities at the molecular level, which render its description a difficult task. For the elucidation of the system's hydrogen bonding features that are the key factors in its complex behavior, we conduct a Density Functional Theory analysis on relevant water/ethanol clusters inside implicit solvent cavities for the determination of the ethanol donor hydrogen bond strength. We record Attenuated Total Reflectance spectra of water/ethanol-OD solutions and utilize our density and refractive index measurements for post-processing. The application of the Badger-Bauer rule reveals a minimum in the strength of the ethanol donor hydrogen bond for a composition of xwater = 0.74. We attempt to analyze further this result by estimating the effect of the implicit solvent on the ethanol donor hydrogen bond strength, finding it to be incremental. A brief analysis of different cluster conformations is carried out to determine the cooperativity conditions that can potentially explain the observed minimum in the ethanol donor hydrogen bond strength. These observations are related to notions of microheterogeneity in water/alcohol mixtures and provide context toward a more elaborate picture of association in heteroclusters.