Non-Aqueous Solvation of n-Octanol and Ethanol:  Spectroscopic and Computational Studies

Raman spectroscopy was used to examine the interactions of the free O−H bonds in n-octanol and ethanol with the organic solvents carbon tetrachloride (CCl4), cyclohexane, and benzene. These spectra reveal that the solvents CCl4 and cyclohexane have a small effect on the free O−H peak of alcohols, whereas benzene as a solvent significantly red-shifts the free O−H band. Calculated spectra were generated via MP2/6-31G* calculations and the B3LYP/6-31+G**//MP2/6-31G*-derived Boltzmann populations of each ethanol complex and are consistent with the experimental results. Additional spectra were calculated using Boltzmann populations derived from single-point energies at the polarizable continuum model (PCM) level with the B3LYP/6-31+G** level of theory to take overall solvent effects into account, and these simulated spectra are also largely consistent with the experimental results. Analysis of the computational results reveals a lengthening of the O−H bond from the O−H interaction with the delocalized electronic structure of benzene as well as a bimodal distribution of the free O−H peak of the alcohol/benzene mixtures due to two distinctly different types of alcohol/benzene complexes.