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Evaluation of the Alicyclic Gauche Effect in 2-Fluorocyclohexanone Analogs: a Combined NMR and DFT Study
European Journal of Organic Chemistry ( IF 2.8 ) Pub Date : 2020-02-11 , DOI: 10.1002/ejoc.201901815
Daniela Rodrigues Silva 1, 2 , Lucas A. Zeoly 3 , Rodrigo A. Cormanich 3 , Célia Fonseca Guerra 2, 4 , Matheus P. Freitas 1
Affiliation  

Herein, we have investigated the effect of an endocyclic group (forming the N–C–C–F fragment) on the conformational preferences of 2-fluorocyclohexanone analogs. A combined approach of nuclear magnetic resonance and density functional theory calculations was employed to assess the conformational equilibrium in several media. In turn, natural bond orbital analysis and the conformational behavior of other 2-halocyclohexanone analogs were used to get more insights about the intramolecular interactions governing the conformer stabilities. Our results reveal that any stabilization from interactions featured in the gauche effect is overcome by a short-range interaction of the fluorine substituent with the carbonyl group. Consequently, the gauche effect in heterocyclic compounds is not as stabilizing as in their acyclic counterparts. Only the electrostatic gauche effect takes place even in polar solvents owing to an attraction between the axial fluorine and an endocyclic quaternary ammonium group.

中文翻译:

评估 2-氟环己酮类似物中的脂环族 Gauche 效应:结合 NMR 和 DFT 研究

在此,我们研究了内环基团(形成 N-C-C-F 片段)对 2-氟环己酮类似物构象偏好的影响。采用核磁共振和密度泛函理论计算的组合方法来评估几种介质中的构象平衡。反过来,自然键轨道分析和其他 2-卤代环己酮类似物的构象行为被用来获得关于控制构象异构体稳定性的分子内相互作用的更多见解。我们的结果表明,由于氟取代基与羰基的短程相互作用,克服了以 gauche 效应为特征的相互作用的任何稳定性。因此,杂环化合物中的 gauche 效应不像它们的无环对应物那样稳定。
更新日期:2020-02-11
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