Dynamic Cross-Exchange in Halophosphonium Species: Direct Observation of Stereochemical Inversion in the Course of an S<sub>N</sub>2 Process
作者:Kirill Nikitin、Elizabeth V. Jennings、Sulaiman Al Sulaimi、Yannick Ortin、Declan G. Gilheany
DOI:10.1002/anie.201708649
日期:2018.2.5
bromides and chlorides R3PX+X− (R=Alk, Ar, X=Cl or Br) were studied by NMR techniques. Their energy barriers are typically ca. 11 kcal mol−1, but rise rapidly as bulky groups are attached to phosphorus, revealing the importance of steric factors. In contrast, electronic effects, as measured by Hammett analysis, are modest (ρ 1.46) but still clearly indicate negative charge flow towards phosphorus in
否则很相似鏻溴化物和氯化物之间的复杂fluxional的互- [R 3 PX + X -通过NMR技术研究(R = ALK中,Ar,X = Cl或Br)。它们的能量壁垒通常约为。11 kcal mol -1,但由于庞大的基团附着在磷上而迅速升高,显示出空间因素的重要性。相反,通过Hammett分析测得的电子效应是适度的(ρ1.46),但仍清楚地表明在过渡态时有负电荷流向磷。最重要的是,对交换路径的详细分析是明确的,并且在任何此类过程中都是第一次,这表明亲核阴离子对四面体中心的亲核攻击导致构型反转。