کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
5376677 1389369 2006 6 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Computational study of keto-enol equilibria of tropolone in gas and aqueous solution phase
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی تئوریک و عملی
پیش نمایش صفحه اول مقاله
Computational study of keto-enol equilibria of tropolone in gas and aqueous solution phase
چکیده انگلیسی
Density functional theory calculations employing the B3LYP exchange-correlation functional, as well as Hartree-Fock computations, were performed on 2-hydroxy-2,4,6-cycloheptatrien-1-one (tropolone) and 3,5- and 3,6-cycloheptadiene-1,2-dione in gas and aqueous solution phases in order to determine the equilibrium constant for keto to enol interconversion of the isomers of C7H6O2. Two standard basis sets were used throughout, namely 6-311++G∗∗ and aug-cc-pVDZ. Solvent effects were modelled using two different self-consistent reaction field approaches - the Onsager dipole and the polarizable continuum models (PCM). In addition, the G3 method was used for calculations on species in the gas phase. Molecular geometries were fully optimized at each model chemistry, and it was found that the two keto isomers are always higher in energy than the enol form. From the results of B3LYP/6-311++G∗∗ calculations of the difference in Gibbs free energy in the gas phase and using PCM, the relative pK values for the 2-hydroxy-2,4,6-cycloheptatrien-1-one ⇆ 3,5- and 3,6-cycloheptadiene-1,2-dione system are 13.75 (g), 15.78 (g) and 13.05 (aq) and 13.45 (aq), respectively. That equilibrium is tilted almost exclusively in the direction of tropolone is due to resonance stabilization of the enol as a result of aromaticity, and is most easily understood on the basis of elementary Hückel theory.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemical Physics - Volume 331, Issue 1, 11 December 2006, Pages 61-66
نویسندگان
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