Knowledge Bank

Vibrational circular dichroism (VCD) spectra of two simple chiral three-membered ring molecules, (S,S)-oxirane-2,3-$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}H2$ and (S,S)-cyclopropane-1,2-$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}H2$ have been obtained for samples in the gas phase and in $C2Cl4$ and $CS2$ solution. Due to electric dipole moment contributions from oxirane ring stretches, the A-symmetry modes are more intense than the B-symmetry modes in the mid-infrared region of (S,S)-oxirane-$2,3-2H2$, whereas the mid-infrared B-symmetry are more intense in (S,S)-cyclopropane-$1,2-\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}H2$. The signs and relative intensities of the VCD bands in both molecules can be understood in terms of chiral perturbation, due to the deuterium substitution, of the parent achiral oxirane or cyclopropane vibrations. This perturbation mixes modes of the parent molecule that involve linear charge oscillation along an axis with modes that involve angular charge oscillation about that same axis. Comparisons will be made of the observed rotational strengths with recent published VCD intensity calculations using various theoretical approaches.""