Infrared spectroscopy of ethanol clusters in ethanol–hexane binary solutions

Abstract

Temperature and concentration dependent infrared spectra were recorded for binary solutions of ethanol–hexane, ethanol–carbon tetrachloride, and ethanol–cyclopentane. The temperature range covered was 198 K to 298 K; concentrations ranged from 0.45 mole percent to 4.0 mole percent ethanol. Changes in the OH stretch frequency are consistent with the formation of ethanol clusters (EtOH)n, where n ranges from 2 to 6. The geometry, OH stretch frequency and proton chemical shift for 14 different ethanol clusters ranging from monomer to hexamer in cyclic and linear arrangements were investigated using density functional methods (B3LYP/6-31+G*). These clusters include both gauche and anticonformers of the monomer unit. The OH stretch frequency calculations were compared to experimental Fourier transform infrared measurements made as a function of concentration and temperature for dilute ethanol in hexane binary mixtures. Analysis of the O–H stretch frequency data (3100 to 3700 cm−1) indicate the presence of small clusters of ethanol. The data indicate that at the lower temperatures the clusters are primarily cyclic tetramers, pentamers, and hexamers. This infrared data is in excellent agreement with recent concentration and temperature dependent nuclear magnetic resonance chemical shift investigations that indicate a dramatic change in cluster size with concentration and temperature.