MID-INFRARED VIBRATIONAL CIRCULAR DICHROISM AND APPLICATIONS OF THE

COUPLED OSCILLATOR MODEL

Su, Eric Chen Nan

Abstract

Vibrational Circular Dichroism (VCD) measurements in the newly accessible mid-infrared region, down in energy to 900 cm^-1, is made possible by using a carbon rod furnace, a HgCdTe detector, a ZnSe modulator and by modifying some optical components. The experimental design of this new VCD spectrometer is discussed in detail.

The VCD spectra of optically active dimethyltartrate and related molecules are used to test and demonstrate the application of a simple theory for VCD, called the "Degenerate Coupled Oscillator" (DCO) model. Some conformational information regarding dimethyltartrate in a dilute, nonhydrogen-bonding solution is drawn from VCD and NMR results.

The VCD spectra of CH₃ deformation modes of phenylethylamine, phenylethyl alcohol, phenylethyl isocyanate and related molecules are measured. They are discussed using the fixed partial charge model of VCD and are compared with the results obtained from Raman circular intensity differential (CID) scattering experiments.

The DCO model is also used to interpret the VCD spectra of (-) 2,2'-dimethyl 6,6'-diaminobiphenyl in terms of its twist angle. Finally VCD spectra of some chiral phosphamide compounds are also presented. Attempts are made to correlate VCD results with the absolute configuration structure of these compounds.