1. Optical Activity of Chiral Epoxides: Influence of Structure & Environment on Intrinsic Chiroptical Response
Paul M. Lemler, Clayton L. Craft, & Patrick H. Vaccaro
Department of Chemistry, Yale University
225 Prospect Street New Haven, CT USA

2. Natural Optical Activity A Brief Overview
Circular Birefringence (CB) : Non-Resonant Differential Retardation
Solution phase optical activity is introduced as an intrinsic property of chiral solute molecule
Solvent-solute interactions can drastically modify observed magnitude & sign†
Quantitative interpretation of CB necessitates interrogation of solvent-free response.
† S. M. Wilson, K.B. Wiberg, M.J. Murphy, and P.H. Vaccaro Chirality 20(3-4), (2008).

3. Cavity Ring-Down Polarimetry
P. H. Vaccaro, Chapter 11 in Comprehensive Chiroptical Spectroscopy, eds. N. Berova, et al. (Wiley, Hoboken, NJ, 012).

4. Systems Currently Being Investigated
RG09
Clayton
Craft
(1S,2S) –Phenylpropylene oxide (PPO)
(R)–3–Methyl–2–Aminobutane (MAB)
(R) –2–Methylpyrrolidine (MPY)
(R)–Styrene oxide (SO)
(S)–3,3–Dimethyl–2–Aminobutane (DMAB)
(S) –2–Methylpiperidine (MPI)
(R)–α–Methylbenzylamine (αMBA)
(S)–Glycidol (GLY)
Methyl–(2S)–Glycidate (MGly)

5. Vibrational Contribution to Optical Activity
Calculate expectation value for each vibrational quantum state:
Determine Boltzmann weight for each quantum state:
Compute collective response for thermal ensemble:

6. Implicit Solvation Model
Polarizable
Continuum
Model
Solvent modeled as dielectric continuum surrounding interlocking van der Waals- spheres centered at atomic positions
Accurately describes long-range electrostatic solute-solvent interactions
Dominated by electrostatic contributions to solvated response, ignoring first-shell interactions which govern short-range interaction terms.
Valued and ubiquitously utilized for its computational expedience stemming from reduced degrees of freedom in comparison to explicit models of solvation

7. Summary and Conclusions
Cavity Ring-Down Polarimetry (CRDP) affords a sensitive probe for elucidating dispersive optical activity (CB) under rarefied gas-phase conditions.
Solvation can influence optical activity in pronounced and counterintuitive ways, modifying both the magnitude and the sign of response evoked from rigid molecules.
Small electronic response of styrene oxide (SO) is perturbed significantly by vibrational contributions and highlights inadequacies of DFT predictions for optical activity.
Implicit solvation models are in good accord with PPO behavior, but show less satisfactory agreement with SO response possibly due to vibrational contributions.
Future efforts will include molecular dynamics simulations to search for solute-solvent complexes combined with more extensive vibrational-averaging analyses.
Supported by
U.S. National Science Foundation