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Computational study of tautomerism and aromaticity in mono- and dithio-substituted tropolone

Authors

  • S. W. Paine,

    1. Department of Chemistry, Wake Forest University, Winston-Salem, North Carolina 27109
    2. Instituto de Quimica, School of Veterinary Medicine and Science, University of Nottingham, Leicestershire LE12 5RD, United Kingdom
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  • A. Salam

    Corresponding author
    1. Department of Chemistry, Wake Forest University, Winston-Salem, North Carolina 27109
    2. Departamento de Quimica Fundamental, Universidade de Sao Paulo, Sao Paulo 05508, Brasil
    • Department of Chemistry, Wake Forest University, Winston-Salem, North Carolina 27109
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Abstract

Keto-enol tautomerism in mono- and dithio-substituted analogs of tropolone was investigated using electronic structure computations. Seven structural isomers of C7H6OS and four of C7H6S2 were optimized fully in gas phase at HF and B3LYP theoretical levels in combination with the 6-311++g** basis set, as well as with the CBS-QB3 and G3 methods. To examine the effects of an aqueous solvent on tautomeric equilibrium constants, each species was optimized in water using the self-consistent reaction field polarizable continuum model at HF/6-311++g** and B3LYP/6-311++g** model chemistries. In both phases it was found that the enol forms were significantly more stable with respect to electronic energy and Gibbs free energy compared to the keto isomers, and outnumbered the keto species by several orders of magnitude. This was understood on the basis of elementary Hückel theory and the 4n + 2 rule, and supported by nucleus independent chemical shifts computations of NMR chemical shifts in these seven membered cyclic systems. © 2012 Wiley Periodicals, Inc.

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