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Not all third-row elements experience the fluorine gauche effect: beta-fluorinated organophosphorus compounds

Abstract

Conformational analyses of beta-fluorinated organophosphorus compounds were theoretically carried out to probe the role of a possible fluorine-phosphorus gauche effect on the conformer stabilization, specifically using a phosphine, a phosphine oxide, phosphinic and phosphonic acids, and the corresponding anions as model compounds. This hypothesis emerged from recent findings for beta-fluorinated sulfoxides, sulfones, and thionium cations, which exhibit the electrostatic gauche effect. Surprisingly, despite bearing a positively charged phosphorus atom, the studied compounds do not show a gauche preference in most gas phase conformers, while little predominance of gauche conformers in solution was calculated only in some cases, due to intramolecular hydrogen bond. Steric and electrostatic repulsive interactions are invoked as dominating effects rather than electrostatic and/or hyperconjugative gauche effects, since the conformational equilibrium in these compounds is better described by a well-balanced competition between anti and gauche conformers. Since the conformational equilibrium is not polarized towards a single conformer, the unusual three-bond coupling constants 3JP,F and 3JP,H can be useful to verify the changes in conformational populations with the solvent, as confirmed by NMR calculations.

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Publication details

The article was received on 07 Jul 2017, accepted on 28 Jul 2017 and first published on 31 Jul 2017


Article type: Paper
DOI: 10.1039/C7NJ02463K
Citation: New J. Chem., 2017, Accepted Manuscript
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    Not all third-row elements experience the fluorine gauche effect: beta-fluorinated organophosphorus compounds

    L. A. F. Andrade and M. de Freitas, New J. Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7NJ02463K

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