The anomalously large chiroptical response of (1R,4R)-norbornenone has been probed under complementary vapor-phase and solution-phase conditions to assess the putative roles of environmental perturbations. Measurements of the specific rotation for isolated (gas-phase) molecules could not be reproduced quantitatively by comprehensive quantum-chemical calculations based on density-functional or coupled-cluster levels of linear-response theory, which suggests that higher-order treatments may be needed to accurately predict such intrinsic behavior. A substantial, yet unexpected, dependence of the dispersive optical activity on the nature (phase) of the surrounding medium has been uncovered, with the venerable Lorentz local-field correction reproducing solvent-mediated trends in rotatory dispersion surprisingly well, whereas more modern polarizable continuum models for implicit solvation performed less satisfactorily.

The anomalously large chiroptical response of (1R,4R)-norbornenone has been probed under complementary vapor-phase and solution-phase conditions to assess the putative roles of environmental perturbations. Measurements of the specific rotation for isolated (gas-phase) molecules could not be reproduced quantitatively by comprehensive quantum-chemical calculations based on density-functional or coupled-cluster levels of linear-response theory, which suggests that higher-order treatments may be needed to accurately predict such intrinsic behavior. A substantial, yet unexpected, dependence of the dispersive optical activity on the nature (phase) of the surrounding medium has been uncovered, with the venerable Lorentz local-field correction reproducing solvent-mediated trends in rotatory dispersion surprisingly well, whereas more modern polarizable continuum models for implicit solvation performed less satisfactorily.

It has been recognized that quantum-chemical predictions of dispersive (nonresonant) chiroptical phenomena are exquisitely sensitive to the periphery of the electronic wavefunction. To further elaborate and potentially exploit this assertion, linear-response calculations of specific optical rotation were performed within the framework of density-functional theory (DFT) by augmenting small basis sets (e.g., STO - 3G and 3 - 21G) for the core and valence electrons with diffuse functions taken from substantially larger bases (e.g., aug-cc-pVXZ where X = D, T, or Q). Of particular interest was the ability of such computationally efficient (augmented small-basis) model chemistries to reproduce results derived from more expensive (canonical large-basis) schemes. The results appear to be quite promising, with the augmented minimal-basis ansatz often yielding wavelength-resolved rotatory powers close to those deduced from standard DFT(B3LYP)/aug-cc-pVXZ treatments. Analogous linear-response analyses were performed by means of coupled-cluster singles and doubles (CCSD) theory, once again leading to augmented small-basis estimates of specific rotation in reasonable accord with their large-basis counterparts. Although CCSD predictions were deemed to be slightly worse than those obtained from DFT, they still were of sufficient quality for such reduced-basis calculations to be considered viable for exploratory work. Chirality 25:606–616, 2013. © 2013 Wiley Periodicals, Inc.

The vapor-phase optical rotation (or circular birefringence) of (S)-1,2-epoxybutane, (S)-epichlorohydrin, and (S)-epifluorohydrin has been measured at the nonresonant excitation wavelengths of 355 nm and 633 nm by means of Cavity Ring-Down Polarimetry (CRDP). Complementary solution-phase studies were performed in a wide variety of dilute solvent media to highlight the pronounced influence of solute–solvent interactions. Density functional theory calculations of optical activity have been enlisted to unravel the structural and electronic provenance of experimental observations. Three stable, low-lying conformers have been identified and characterized for each of the targeted chiral species, with thermal (relative population weighted) averaging of their antagonistic chiroptical properties allowing specific rotation values to be predicted under both isolated and solvated conditions. For (S)-epichlorohydrin and (S)-epifluorohydrin, a self-consistent isodensity polarizable continuum model (SCI-PCM) has been exploited to gain further insight into the underlying nature of solvation effects. Chirality, 2008. © 2007 Wiley-Liss, Inc.