Computer-aided simulation of infrared spectra of ethanol conformations in gas, liquid and in CCl4 solution

The recently developed efficient protocol combining implicit and explicit, accurate quantum-mechanical modeling of the condensed state (Katsyuba et al., J. Chem. Phys. 155, 024507 [2021]) is used to describe the IR spectra of liquid ethanol and its solutions in CCl4. The relative abundance of the anti and gauche conformers of ethanol is shown to increase from similar to 40:60 in the gas phase to similar to 55:45 in the liquid phase. In spite of a moderate impact of media effects on the conformational composition of the liquid, the solvent strongly influences vibrational frequencies, IR intensities, and normal modes of each conformer, producing qualitatively different spectra compared to the gas phase and CCl4 solution. Further, these solvent effects affecting IR frequencies and intensities depend not only on the conformation of the solvated molecule but also on the solvating species. Nevertheless, vibrational frequencies of anti and gauche conformers of liquid ethanol and its several isotopomers practically coincide with each other. Convenient liquid-state conformational markers in the fingerprint region of IR spectra are revealed for the hydroxyl-deuterated species: CH3CH2OD, CH3CHDOD, CH3CD2OD, and CD3CD2OD.

Automated summary

The study utilizes an efficient protocol to describe the IR spectra of liquid ethanol and its solutions in CCl4, revealing changes in ethanol conformers in different phases and significant solvent effects on vibrational frequencies and intensities.