Optical Activity of Vibrational Origin. II. Consequences of Polymer Conformation

Abstract
Calculations of absorption, circular dichroism, and optical rotatory dispersion spectra associated with vibrational transitions of several idealized helical polymers are reported. Although specific assumptions are made regarding the vibrational force field and the charge distribution within the polymer, these assumptions are applied consistently in an investigation of the effects of chain length and helical conformation upon the optical properties. Results obtained for an idealized model of polypropylene indicate that even rather short helical segments (5–10 residues) may have spectra rather similar to those calculated for an infinite helix. Calculations performed for several polypropylene oxide models indicate that the optical rotatory dispersion and circular dichroism spectra may, in some cases, be more sensitive to small changes in the helix geometry than the absorption spectra. Furthermore, in these instances a number of the partial ORD curves exhibit the characteristic triple‐extrema shape which may be associated with transitions polarized perpendicularly to the helix axis. The potential usefulness of infrared optical activity measurements in assigning vibrational spectra and in determining polymer conformations is discussed.