Conformational stability of (+)-epichlorohydrin

Vibrational absorption and circular dichroism spectra of (+)-epichlorohydri n have been recorded for the neat liquid and in organic solvents CCl4 CS2, CHCl3, CH2Cl2, and CH3I. These spectra are compared with the ab initio pred ictions of absorption and vibrational circular dichroism (VCD) spectra obta ined with density functional theory using the B3LYP/6-311G(2d,2p) basis set for three different conformers of (S)-epichlorohydrin. The Boltzmann popul ations, obtained from Gibbs free energies, indicate that the populations of gauche-II, gauche-I, and cis conformers for isolated molecule are 65, 32, and 3%, respectively. The analysis of experimental and theoretical absorpti on data indicates that the population ratios of conformers gauche-II:gauche I:cis are: similar to 35.7%:similar to 54.6%:9.7% (neat liquid); similar t o 58.6% :similar to 34.0%:7.4% (CCl4); similar to 51.0%:similar to 40.6%: 8 .4% (CS2); similar to 46.1%: similar to 44.8%:9.1% (CHCl3); similar to 42.2 %:similar to 48.5%:9.3% (CH3I); similar to 37.2%:similar to 53.3%:9.5% (CH2 Cl2). These compositions are consistent with the experimental VCD spectra. This information clearly indicates that as the polarity of the solvent (as measured by its dipole moment) is increased, the percent composition of the gauche I form increases and that of the gauche II form decreases, but that of cis form is nearly the same in all cases. Vibrational assignments are s uggested for the observed bands in the 1500-400-cm(-1) region, with the fun damentals assigned mainly to the gauche-II and gauche-I conformers.