Revealing structure, dynamics and chirality of polar molecules

We perform chirality-sensitive broadband microwave spectroscopy on a conformational mixture, distinguishing enantiomers, measuring enantiomeric excesses, and determining the absolute configurations of the enantiomers of carvone [1]. Our method uses microwave three-wave mixing and is inherently mixture-compatible [2], a unique advantage over other techniques and particularly interesting for applications. In contrast to conventional microwave spectroscopy, we also exploit the phase of the received signal. This phase depends upon the signs of the molecules’ dipole-moment components and is used to identify the excess enantiomer. The measured signal amplitude determines the size of the excess. We use our broadband capabilities to simultaneously excite and measure two conformers of carvone, demonstrating analysis of a sample with multiple chiral species. Employing quantum chemical calculations and the measured phases, the absolute configurations of the enantiomers are determined. From the pure rotational spectra obtained, precise information about the molecular structure and intramolecular dynamics can be obtained.

1. V.A. Shubert, D. Schmitz, D. Patterson, J.M. Doyle, M. Schnell Angewandte Chemie Int. Ed. (2013) accepted.
2. D. Patterson, M. Schnell, J.M. Doyle Nature 497 (2013) 475.