An experimental FTIR-ATR and computational study of H-bonding in ethanol/water mixtures

Ethanol/water mixtures have served as a model to study the hydrophobic effect and the formation of clathrate and other cage like water formations around the hydrophobic end of ethanol. We have studied the evolution of FTIR-ATR spectra of ethanol/water mixtures as a function of the content of water in the mixture. The experimental spectra show redshift of primarily the H-O-H bending vibration, which is 18.9 cm−¹ in total width. It also shows a blueshift of 9.0 cm−¹ of the asymmetric stretching vibration of C-H groups of β-CH₃. These infrared spectral shifts are consistent with the formation of a cyclic H-bonded network between ethanol and H-bonded water molecules. This hypothesis has been supported by full optimizations of high-level B3LYP/aug-cc-pVQZ calculations in implicit and explicit water and ethanol solvents as well as MMFF94s simulations of ethanol in explicit water clusters with up to 30 water molecules.