Conformational analysis of 2-halocyclopentanones by NMR and IR spectroscopies and theoretical calculations

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• 作者：Carina R. Martins ; Lucas C. Ducati ; Clá ; udio F. Tormena ; Roberto Rittner
• 关键词：Conformational analysis ; NMR spectroscopy ; Theoretical calculations ; 2-Halocyclopentanones
• 刊名：Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
• 出版年：2009
• 出版时间：June 2009
• 年：2009
• 卷：72
• 期：5
• 页码：1089-1096
• 全文大小：792 K

文摘

The conformational isomerism of 2-chlorocyclopentanone and 2-bromocyclopentanone has been determined through the solvent dependence of the ¹H NMR ³J_HH coupling constants, theoretical calculations and infrared data, using the solvation theory for the treatment of NMR data. In 2-chlorocyclopentanone, the energy difference (E_Ψ-e − E_Ψ-a), in the isolated molecule at B3LYP level of theory, between the pseudo-equatorial (Ψ-e) and pseudo-axial (Ψ-a) conformers is 0.42 kcal mol⁻¹, which decreases in CCl₄ and in acetonitrile solutions, in good agreement with infrared data (ν_CO), despite the uncertainties of the latter method. The conformational equilibrium for 2-bromocyclopentanone is also between the Ψ-e and Ψ-a conformations, with an energy difference (E_Ψ-e − E_Ψ-a), in the isolated molecule at B3LYP level of theory, is 0.85 kcal mol⁻¹ which decreases in CCl₄ and in acetonitrile solutions, also in good agreement with infrared data.