A Kinetic Evaluation of Carbon−Hydrogen, Carbon−Carbon, and Carbon−Silicon Bond Activation in Benzylic Radical Cations
作者:Mauro Freccero、Albert Pratt、Angelo Albini、Conor Long
DOI:10.1021/ja970940s
日期:1998.1.1
A detailed study of the competition between C−C, C−H, and C−Si bond fragmentation in a series of 4-methoxy-α-substituted toluene radical cations (1•+), involving both product studies and kinetic analysis, is presented. C−C bond fragmentation occurs with several radical cations in acetonitrile. The rate constants for such processes, determined by laser flash photolysis, varied from 2.8 × 104 (1c•+)
对一系列 4-甲氧基-α-取代的甲苯自由基阳离子 (1•+) 中 C-C、C-H 和 C-Si 键断裂之间竞争的详细研究,包括产品研究和动力学分析,是呈现。乙腈中的几个自由基阳离子会发生 C-C 键断裂。此类过程的速率常数由激光闪光光解确定,从 2.8 × 104 (1c•+) 到 1.53 × 106 (1f•+) s-1 不等。C-C 键断裂的活化参数的特点是低活化焓约为 30 kJ mol-1,负活化熵在 -34 至 -55 J mol-1 K-1 范围内。自由基阳离子的去质子化始终是由亲核试剂 [硝酸铈 (IV) 硝酸铵 (CAN) 或硝酸根阴离子] 诱导的二级过程,二级速率常数从 7.7 × 107 (1h•+) 到 8。8 × 108 (1i•+) M-1 s-1 在纯乙腈中(CAN 辅助)和从 0.4 × 108 (1j•+) 到 7.1 × 108 (1i•+) M-1 s-1