Identifying Enantiomers in Mixtures of Chiral Molecules with Broadband Microwave Spectroscopy

Authors

  • Dr. V. Alvin Shubert,

    1. Max-Planck-Institut für Struktur und Dynamik der Materie, Luruper Chaussee 149, 22761 Hamburg (Germany)
    2. Center for Free-Electron Laser Science, Notkestrasse 85, 22607 Hamburg (Germany)
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  • David Schmitz,

    1. Max-Planck-Institut für Struktur und Dynamik der Materie, Luruper Chaussee 149, 22761 Hamburg (Germany)
    2. Center for Free-Electron Laser Science, Notkestrasse 85, 22607 Hamburg (Germany)
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  • Dr. David Patterson,

    1. Department of Physics, Harvard University, Cambridge, MA (USA)
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  • Prof. John M. Doyle,

    1. Department of Physics, Harvard University, Cambridge, MA (USA)
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  • Dr. Melanie Schnell

    Corresponding author
    1. Max-Planck-Institut für Struktur und Dynamik der Materie, Luruper Chaussee 149, 22761 Hamburg (Germany)
    2. Center for Free-Electron Laser Science, Notkestrasse 85, 22607 Hamburg (Germany)
    3. The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)
    • Max-Planck-Institut für Struktur und Dynamik der Materie, Luruper Chaussee 149, 22761 Hamburg (Germany)

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  • Financial support from the Fonds der Chemischen Industrie, the Deutsche Forschungsgemeinschaft, and the United States Department of Energy is acknowledged.

Abstract

Chirality-sensitive broadband microwave spectroscopy was performed on mixtures of carvone enantiomers and conformers to distinguish enantiomers, measure enantiomeric excesses, and determine the absolute configurations of the enantiomers. This method uses microwave three-wave mixing and is inherently well-suited to the analysis of mixtures—a unique advantage over other techniques. In contrast to conventional microwave spectroscopy, the phase of the received signal is also exploited. 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. The broadband capabilities of the spectrometer were used to simultaneously excite and measure two conformers of carvone, demonstrating the analysis of a sample with multiple chiral species. Employing quantum chemical calculations and the measured phases, the absolute configurations of the enantiomers are determined.

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