Vibrational circular dichroism, predominant conformations, and hydrogen bonding in (S)-(-)-3-butyn-2-ol

Vibrational absorption and circular dichroism spectra of (S)-(-)-3-butyn-2- ol have been measured in CCl4 solutions in the 2000-900 cm(-1) region. Expe rimental spectra obtained at different concentrations are compared with the ab initio predictions of absorption and VCD spectra obtained with density functional theory using B3LYP/6-31G* basis set for three different conforme rs of (S)-(-)-3-butyn-2-ol. The Boltzmann populations, obtained from Gibbs free energies, indicate the presence of two predominant conformations for t he isolated molecule. The population-weighted theoretical spectra are in sa tisfactory agreement with the experimental spectra obtained at dilute conce ntrations. The influence of intermolecular hydrogen bonding is seen in the experimental spectra at higher concentrations, where a single conformation appears to be predominant. A vibrational analysis was also undertaken for a ll three conformers and vibrational assignments were proposed for the obser ved bands.