Analysis of Vibrational Circular Dichroism Spectra of (S)-(+)-2-Butanol by Rotational Strengths Expressed in Local Symmetry Coordinates

The vibrational circular dichroism (VCD) spectra of (S)-(+)-2-butanol have been observed in dilute CS2 solutions. Two strong VCD bands are assigned mainly to the OH bending modes with the aid of quantum chemical calculations. The calculated VCD spectra corresponding to these bands are shown to depend on the conformation of the OH group. To understand this feature, we have calculated the contribution of each local vibrational mode to the rotational strengths and concluded that the coupling of the group vibrations between the in-plane and out-of-plane modes about the locally assumed symmetry planes play a significant role in VCD. This finding has provided a new scope of VCD in relation to molecular vibrations.