Vibrational Optical Activity

Abstract

While the measurements of optical activity in electronic transitions are widely known and routine, similar measurements pertaining to vibrational transitions became feasible only recently. The vibrational optical activity (VOA) measurements can now be carried out with greater confidence owing to the rapid developments in both instrumentation and theory. The emergence of VOA, as a combination of two widely practiced branches of science namely vibrational spectroscopy and optical activity, offered new pathways for understanding the molecular stereochemistry. Despite its very weak nature, VOA is believed to surpass the conventional electronic optical activity (EOA) in both informational content and complexity. This is because in EOA studies one has to depend upon a limited number of accessible electronic transitions, whereas in VOA studies all 3N-6 vibrational transitions, where N is the number of atoms, of a chiral molecule are available for probing the molecular structure. This increased number of transitions also increases the complexity in interpreting the VOA spectra, but one hopes to find selectivity in structural determination. Since different vibrations encompass different portions of a molecule, the three dimensional view at a particular portion of the molecule may be derived from the VOA associated with the vibrations encompassing that portion. In this way one can hope to selectively determine the stereochemistry and assemble this information for determining the three dimensional structure of the entire molecule.