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Journal Article

The Conformational Map of Volatile Anesthetics: Enflurane Revisited


Pérez,  Cristóbal
Structure and Dynamics of Cold and Controlled Molecules, Independent Research Groups, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Department of Chemistry, University of Virginia, McCormick Rd., Charlottesville, Virginia 22904 (USA);

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Pérez, C., Caballero-Mancebo, E., Lesarri, A., Cocinero, E. J., Alkorta, I., Suenram, R. D., et al. (2016). The Conformational Map of Volatile Anesthetics: Enflurane Revisited. Chemistry – A European Journal, 22(28), 9804-9811. doi:10.1002/chem.201601201.

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Previous ambiguities in the conformational and structural landscape of the volatile anesthetic enflurane have been solved combining microwave spectroscopy in a jet expansion and ab initio calculations. The broadband (2–18 GHz) rotational spectra identified three different rotamers, sharing a common trans ether skeleton but differing in the ±gauche/trans position of the terminal chlorine atom. For each chlorine conformation two different gauche orientations were predicted for the opposite difluoromethyl group, but only one is experimentally observable due to collisional relaxation in the jet. The experimental dataset comprised nine different isotopologues (35Cl, 37Cl, 13C) and a large number (>6500) of rotational transitions. The inertial data provided structural information using the substitution and effective procedures. The structural preferences were rationalized with additional ab initio, natural-bond-orbital and non-covalent-interaction analysis, which suggest that plausible anomeric effects at the difluoromethyl group could be overridden by other intramolecular effects. The difluoromethyl orientation thus reflects a minimization of inter-fluorine repulsions while maximizing F⋅⋅⋅H attractive interactions. A comparison with previous electron diffraction and spectroscopic data in the gas and condensed phases finally resulted in a comprehensive description of this ether, completing a rotational description of the most common multi-halogenated anesthetics.