Chapter 16 - Raman optical activity

Abstract

This chapter discusses optical activity measurements. Chiroptical spectroscopic techniques are particularly useful in chemistry and biology. The most widely known of these, optical rotation and ultraviolet circular dichroism (UVCD), measure electronic optical activity, and are routinely applicable to most chiral molecules under a wide range of sample conditions. Advances in instrument design and technology have led to the extension of optical activity measurements into the vibrational spectrum using both Raman and infrared techniques. Vibrational circular dichroism (VCD) is also a measure of vibrational optical activity; it differs from Raman optical activity (ROA) as it is a measure of the differential absorption of left- and right-circularly polarized infrared radiation, whereas ROA is a measure of the differential inelastic scattering of right- and left-circularly polarized visible radiation. The generation of ROA involves interactions between the chiral molecule and the incident radiation that are of lower order than those that generate VCD. As a result of this difference in mechanism, the ROA and VCD, bands associated with a particular normal mode of vibration usually show a completely different vibrational optical activity. The chapter outlines the theory and practice of ROA spectroscopy through its application to a diverse range of molecules.