How many solvent molecules are required to solvate chiral 1,2-diols with hydrogen bonding solvents? A VCD spectroscopic study.

Strong solute-solvent interactions have been shown to have a significant influence on the vibrational circular dichroism (VCD) spectral signatures of chiral solutes. In order to use VCD spectroscopy to determine absolute configurations, these intermolecular interactions thus need to be accounted for in spectra simulations. For hydrogen bond donating functional groups such as carboxylic acids or hydroxy groups, it has been shown that micro-solvation with a single solvent molecule is usually sufficient to model the effect of the solvent on the vibrational spectra. In the case of diols, however, solvent molecules are competing against the intramolecular hydrogen bond. Therefore, this study investigates the influence of solute-solvent interactions on the conformational preferences and VCD spectroscopic features of chiral 1,2-diols with the aim to answer the title question. We show that both mono- and twofold solvation lead to unique spectral features that can be distinguished experimentally. Furthermore, in the context of absolute configuration determinations, the results of the study suggest that it will not be possible to derive a general rule that is able to tell whether one or two solvent molecules need to be considered explicitly in the simulation of VCD spectra.