Conformational Stability, r0 Structural Parameters, Ab Initio Calculations, and Vibrational Assignment for Fluorocyclopentane

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• 作者：James R. Durig ; Ahmed M. El Defrawy ; Arindam Ganguly ; Todor K. Gounev ; Gamil A. Guirgis
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：September 3, 2009
• 年：2009
• 卷：113
• 期：35
• 页码：9675-9683
• 全文大小：278K
• 年卷期：v.113,no.35(September 3, 2009)
• ISSN：1520-5215

文摘

The infrared spectra (3200−50 cm⁻¹) of the gas and solid and the Raman spectrum (3200−30 cm⁻¹) of liquid and solid fluorocyclopentane, c-C₅H₉F, have been recorded. Additionally the infrared spectra (3200−400 cm⁻¹) of liquid xenon solutions have been recorded at −65 and −95 °C. In all of the physical states, only the twisted C₁ conformer was detected. Ab initio calculations utilizing various basis sets up to MP2(full)/6-311+G(2df,2pd) with and without diffuse functions have been used to predict the conformational stabilities. These calculations predict only the twisted C₁ conformer as the stable form. The two envelope (C_s symmetry) forms with axial and equatorial structures were predicted to be first order saddle points with average higher energies of 75 ± 33 and 683 ± 44 cm⁻¹, respectively, from the C₁ conformer but lower energies of 2442 and 1812 cm⁻¹, respectively, than the planar form by MP2 calculations. Similar values were obtained from the corresponding density functional theory calculations by the B3LYP method. A complete vibrational assignment is given for the twisted (C₁) conformer which is supported by normal coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations. The adjusted r₀ structural parameters have been obtained by systematically fitting the MP2(full)/6-311+G(d,p) predicted values with the rotational constants obtained from a microwave study. The determined heavy atom r₀ distances in Å are (C₁C₂) = 1.531(3), (C₁C₃) = 1.519(3), (C₂C₄) = 1.553(3), (C₃C₅) = 1.533(3), (C₄C₅) = 1.540(3), and (C₁F₆) = 1.411(3) and the angles in degrees are C₃C₁C₂ = 105.5(5), C₁C₂C₄ = 106.2(5), C₁C₃C₅ = 102.9(5), F₆C₁C₂ = 108.9(5), and F₆C₁C₃ = 107.6(5) with a dihedral angle C₂C₄C₅C₃ = 25.3(3). These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.