Dispersive optical activity: Intrinsic response & extrinsic perturbations

Quantitative measurements of optical activity long have been a standard means for assessing enantiomeric purity and assigning absolute configuration. Such analyses typically are performed in the condensed phase, where chiroptical response can be altered markedly by bulk environmental effects and/or specific (solute-solvent) interactions. To alleviate such perturbations and facilitate fundamental studies of natural optical activity, the techniques of cavity ring-down polarimetry (CRDP)¹ have been exploited to measure the intrinsic non-resonant polarization rotation (electronic circular birefringence or ECB) of chiral molecules under rarefied (vapor-phase) conditions. Building on the unprecedented sensitivity afforded by folding kilometer-long pathlengths into a table-top polarimetric instrument, the present work will focus on the ECB signatures of methyloxirane derivatives – deceptively simple species that have been shown to undergo dramatic solvation processes that are capable of changing both the magnitude and the sign of wavelength-resolved rotatory powers. A variety of experimental results obtained in solution-phase (solvated) and vapor-phase (isolated) environments will be highlighted, with complementary quantum-chemical calculations performed at density functional and coupled-cluster levels of theory, serving to interpret findings in terms of electronic structure and vibrational landscape.

(1) Vaccaro P. H. Chapter 11: Optical Rotation and Intrinsic Optical Activity. In: Berova N., Polavarapu P. L., Nakanishi K., Woody R. W., editors. Comprehensive Chiroptical Spectroscopy. Volume 1. Hoboken, NJ: John Wiley & Sons, Inc.; 2012. pp. 275-323.