Chapter 5 - Vibrational Optical Activity in Chiral Analysis

Abstract

Vibrational optical activity comprised of infrared vibrational circular dichroism (VCD) and vibrational Raman optical activity (ROA), was discovered experimental in the early 1970s. Today VCD and ROA supplement the pre-existing chiroptical methods of optical rotation (OR) and electronic circular dichroism (ECD). Although more time consuming to measure, VCD and ROA are much richer in structural information than conventional electronic optical activity. VCD and ROA instrumentation, as well as software for calculations, is now widely available commercially for general use in chiral analysis. The principal applications of VCD is the determination of absolute configuration, achieved by comparing measured and calculated spectra for agreement of signs and relative intensities in the many transitions in each spectrum. VCD is also used for the determination of enantiomeric excess (ee), and by using chemometrics it is possible to follow changes in ee simultaneously in more than one chiral species during a chemical reaction. The principal application of ROA is conformational analysis, although VCD is also used widely as well particularly for following the development of supramolecular chirality in protein amyloid fibrils. Recently the use of broadband Fourier transform microwave spectroscopy for chiral analysis has been reported having a number of potentially unique advantages. Ongoing advances in VOA instrumental and computational methods will further the use of VOA in chiral analysis in the future.