How do Pseudoenantiomers Structurally Differ in the Gas Phase? An IR/UV Spectroscopy Study of Jet-Cooled Hydroquinine and Hydroquinidine

Authors

  • Dr. Ananya Sen,

    1. CNRS, Institut des Sciences Moléculaires d'Orsay (ISMO), UMR8214, Orsay, F-91405 and Univ Paris-Sud, Orsay, F-91405 (France)
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  • Dr. Valeria Lepere,

    1. CNRS, Institut des Sciences Moléculaires d'Orsay (ISMO), UMR8214, Orsay, F-91405 and Univ Paris-Sud, Orsay, F-91405 (France)
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  • Dr. Katia Le Barbu-Debus,

    1. CNRS, Institut des Sciences Moléculaires d'Orsay (ISMO), UMR8214, Orsay, F-91405 and Univ Paris-Sud, Orsay, F-91405 (France)
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  • Prof. Dr. Anne Zehnacker

    Corresponding author
    1. CNRS, Institut des Sciences Moléculaires d'Orsay (ISMO), UMR8214, Orsay, F-91405 and Univ Paris-Sud, Orsay, F-91405 (France)
    • CNRS, Institut des Sciences Moléculaires d'Orsay (ISMO), UMR8214, Orsay, F-91405 and Univ Paris-Sud, Orsay, F-91405 (France)

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Abstract

The gas-phase structures of the cinchona alkaloids, hydroquinine and its pseudoenantiomer hydroquinidine, are studied in a supersonic expansion by means of laser-induced fluorescence and IR/UV double-resonance spectroscopy. Vibrational spectroscopy combined with density functional calculations show that the conformational properties of the two pseudoenantiomers are identical. In both cases, they exist in two isoenergetic forms, with similar IR spectra. Both conformers are similar to the most stable cis-γ-open form of quinine; they differ from each other by the position of the ethyl substituent attached to the quinuclidine ring. Further differences between the two conformers are observed in the laser-induced fluorescence spectrum. The first electronic transition is characterized by time-dependent density functional theory and RI-cc2 calculations, and is of ππ* nature. The results described here emphasize the role of the ethyl substituent in the structural differences between pseudoenantiomers of cinchona alkaloids.

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