Endocyclic Oxygen in 3-Fluorodihydro-2H-pyran-4(3H)-one That Does Not Induce the Gauche Effect

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• 作者：Thayn谩 F. B. Silva ; Laize A. F. Andrade ; Josu茅 M. Silla ; Claudimar J. Duarte ; Roberto Rittner ; Matheus P. Freitas
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：August 14, 2014
• 年：2014
• 卷：118
• 期：32
• 页码：6266-6271
• 全文大小：300K
• ISSN：1520-5215

文摘

2-Fluorocyclohexanone undergoes chair inversion, giving rise to axial and equatorial conformers, with the equatorial form being highly preferred in solution, for example, 87% in chloroform and 93% in methylene chloride. Modifications in the conformational preferences can modify macroscopic properties of 2-fluoro ketones. The introduction of an endocyclic oxygen in 2-fluorocyclohexanone to give 3-fluorodihydro-2H-pyran-4(3H)-one would be expected to create a gauche effect in the axial conformer along with the O鈥揅鈥揅鈥揊 moiety, inducing an increase of its population. However, small changes were verified in the conformational populations both in the gas phase and solution because the carbonyl group plays an important role for the hyperconjugation in the equatorial conformer, despite experiencing strong dipolar repulsion with the fluorine atom. These data were obtained theoretically and by NMR spectroscopy, while the nature of the interactions governing these conformational shifts were investigated on the basis of natural bond orbital analysis.