Predominant conformations of (2R,3R)-(-)-2,3-butanediol

Vibrational absorption and circular dichroism spectra of (-)-2,3-butanediol have been measured in CS2 and CCl4 solutions in the 2000-900 cm(-1) region. Experimental spectra obtained at different concentrations are compared with the ab initio predictions of absorption and circular dichroism spectra obtained with density functional theory using the B3LYP/6-31G* basis set for different conformers of (2R,3R)-2,3-butanediol. The Boltzmann populations, obtained from Gibbs free energies, indicate the presence of 10 predominant conformations for isolated molecules. The conformational stability of (2R,3R)-(-)-2,3-butanediol in dilute solution is also investigated on the basis of calculations with self-consistent reaction field (SCRF) methods. The population-weighted theoretical spectra are in satisfactory agreement with the experimental spectra obtained at dilute concentrations. Intramolecular hydrogen bonding in (2R,3R)-(-)-2,3-butanediol is observed in the dilute solution, and intermolecular hydrogen bonding is evident in the experimental spectra at higher concentrations. Solvent influence on the absorption and circular dichroism spectra is also presented.