A QTAIM-based energy partitioning for understanding the physical origin of conformational preferences: Application to the Z effect in O=C-X-R and related units

Authors

  • David Ferro-Costas,

    1. Departamento de Química Física, Universidade de Vigo, Facultade de Química, Lagoas-Marcosende s/n, 36310 Vigo, Galicia, Spain
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  • Nicolás Otero,

    1. Departamento de Química Física, Universidade de Vigo, Facultade de Química, Lagoas-Marcosende s/n, 36310 Vigo, Galicia, Spain
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  • Ana M. Graña,

    1. Departamento de Química Física, Universidade de Vigo, Facultade de Química, Lagoas-Marcosende s/n, 36310 Vigo, Galicia, Spain
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  • Ricardo A. Mosquera

    Corresponding author
    1. Departamento de Química Física, Universidade de Vigo, Facultade de Química, Lagoas-Marcosende s/n, 36310 Vigo, Galicia, Spain
    • Departamento de Química Física, Universidade de Vigo, Facultade de Química, Lagoas-Marcosende s/n, 36310 Vigo, Galicia, Spain
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Abstract

A quantum theory of atoms in molecules-based energy partitioning was carried out for Z and E conformers of a series of O=C-X-R containing compounds. The results obtained for the simplest compound (formic acid) indicate that the attraction of the electron density within carbonyl oxygen by the nucleus of the acid hydrogen is the most important energy term for Z preference. This conclusion can be extended (mutatis mutandis) to larger carboxylic acids, esters, sulfur derivatives, secondary amides, and carbonyl isocyanates, and even explains the sequence of relative conformational energies in the HCXOH series (X = O, S, Se). In contrast, although the hyperconjugative model has been traditionally employed to explain this preference, we observe it is incompatible with: (i) relative values of diverse QTAIM atomic populations for the Z/E conformational equilibrium; (ii) conformational energies in the HCXOH series. © 2012 Wiley Periodicals, Inc.

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