Ohta Brian K, Hough Ruth E, Schubert Jeffrey W
Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085, USA.
Org Lett. 2007 Jun 7;9(12):2317-20. doi: 10.1021/ol070673n. Epub 2007 May 8.
Isotopic perturbation of degenerate equilibrium is used to determine whether tetramethylethylenechloronium and tetramethylethylenebromonium ions are closed 1,2-bridged structures or rapid equilibria of open beta-halocarbenium ions. The observed 13C NMR isotope shifts are consistent with a combination of large equilibrium shifts and small upfield intrinsic shifts. The presence of equilibrium shifts in both halonium ions indicates that these ions are not closed 1,2-bridged structures. Rather, they are best represented by equilibria of beta-halocarbenium ions.
简并平衡的同位素扰动用于确定四甲基乙烯氯鎓离子和四甲基乙烯溴鎓离子是封闭的1,2 - 桥连结构还是开放的β-卤代碳鎓离子的快速平衡。观察到的13C NMR同位素位移与大的平衡位移和小的场内向本征位移的组合一致。两种卤鎓离子中都存在平衡位移，这表明这些离子不是封闭的1,2 - 桥连结构。相反，它们最好用β-卤代碳鎓离子的平衡来表示。
