Electronic and Steric Effects on the Reactivity of Seleniranium Ions with Alkenes in the Gas Phase
作者:Samuel C. Brydon、Catriona Thomson、Richard A. J. O’Hair、Jonathan M. White
DOI:10.1021/acs.joc.2c02233
日期:——
Gas phase ion-molecule reactions between seleniranium ions, R-c-SeCH2CH2+, and cis-cyclooctene were used to probe electronic and steric effects of substituents on kinetics and branching ratios. The second-order rate coefficients increased in the order p-OMeC6H4 < C6H5 < p-BrC6H4 < p-CF3C6H4 < m-NO2C6H4, giving a Hammett plot with R2 = 0.98 and ρ = +1.66. The two main pathways include direct transfer
使用硒离子、R- c -SeCH 2 CH 2 +和顺式环辛烯之间的气相离子-分子反应来探测取代基对动力学和支化比的电子和空间效应。二阶速率系数按p -OMeC 6 H 4 < C 6 H 5 < p -BrC 6 H 4 < p -CF 3 C 6 H 4 < m -NO 2 C 6 H 4的顺序增加,给出 Hammett绘制R 2 = 0.98 且 ρ = +1.66 的图。两个主要途径包括将硒部分直接转移到传入的烯烃(π-配体交换)和不太有利的通过攻击伊朗碳进行开环以得到由密度泛函理论(DFT)支持的顺式双环硒离子)计算。每个途径的分支比表明,吸电子基团对碳的攻击比对硒的攻击更多,这与之前的溶液相结果一致。通过将 R 基团从甲基更改为叔丁基来研究硒上空间体积的增加,这不仅关闭了 π-配体交换,而且还显着降低了整体反应性。最后,研究了源自Se-甲基硒代半胱氨酸的伊朗离子的反应性,结果表