定性地说,与单环供体 11a*b 相比,双环供体的较小 V 表明轨道重叠积分较小,并且与较大芳族系统的分子轨道的更复杂节点结构导致更小的基质元素的预测一致。 'Ic 对于单环化合物,较大的 A 表明与双环化合物相比,这些双环化合物的溶剂化程度更高。从 exciplex 发射数据中获得了对该建议的支持。尽管激基复合物的溶剂化程度不如双生对,但这些物质可以被认为是溶剂渗透双生对的接触离子对等价物。 '2 因此,从不同极性溶剂中发射最大值的差异获得的激基复合物溶剂化,可用作双子对溶剂化的指南。在乙腈和环己烷中 DCA 与双环化合物 1-3 的激发态发射中发现了 0.345 f 0.013 eV 的恒定能量差。对于这两种溶剂中单环供体的相应激基复合物,发现了 0.49 f 0.02 eV 的恒定且更高的值,这与这些情况下的较高溶剂化一致。这些系统中的返回电子转移率 k,,, 显然对小的结构变化非常
Enolization of Aldehydes and Ketones: Structural Effects on Concerted Acid−Base Catalysis
作者:Anthony F. Hegarty、Joseph P. Dowling、Stephen J. Eustace、Michelle McGarraghy
DOI:10.1021/ja9729544
日期:1998.3.1
the product of the consecutive rate constants (kA·kB) and the concerted (third order) rate constants (kAB). This implies that the concerted pathway is important only when both the generalacid and the generalbase terms are significant; this will be useful in designing other systems which might show such concertedcatalysis. In the case of aldehydes, a slope of 0.97 was found for this plot, which compares
The kinetics of oxidation of 2-propanone, 2-butanone, 2-pentanone, 3-pentanone, and 4-methyl-2-pentanone by sodium salt of N-bromo-p-toluenesulfonamide or bromamine-T (BAT) in presence of HClO4 was studied at 30 °C. The rate law is: −\fracd[BAT]dt=k[BAT]0[ketone]1[H+]1. Variation of ionic strength of medium or addition of reaction product p-toluenesulfonamide have no effect on the rate. The dielectric