Kinetic study of the proton transfer reaction between (2,6-dialkyl-4-nitrophenyl)phenylcyanomethanes and MTBD in acetonitrile
作者:Kazimierz Minksztym、Arnold Jarczewski
DOI:10.1016/j.molstruc.2003.12.021
日期:2004.3
charge distribution between 4-nitrophenyl and cyano substituents. The observed kinetics reflect superposition of the properties of substituents, including ortho -alkyls and solvation effect on the transition state (TS) in acetonitrile. The general view is that the TS comes early along the reaction path. The possible structure of the TS and the general discussion of the mechanism are given.
摘要 合成了三种(2,6-二烷基-4-硝基苯基)苯基氰基甲烷(烷基=Me-1、Et-2、i-Pr-3)并用于乙腈中强MTBD碱提取质子的动力学研究。这些碳酸:1、2和3在乙腈中显示出相似的强度,分别具有p K a =25.78、25.94、26.19。1 k H 25° =141.2 dm 3 mol -1 s -1 反应最快,2 k H 25° =65.9 dm 3 mol -1 s -1 反应最慢,而3接近二乙基衍生物k H 25° =67.9 dm 3 mol -1 s -1 。主要氘动力学同位素效应 k H / k D 的值适中,对大量烷基取代基不敏感,在 10–35 °C 的温度范围内,1 的范围为 11 至 16,3 的范围为 12 至 13。根据烷基对4-硝基苯基和氰基取代基之间电荷分布的立体电子影响,讨论了C-酸的酸度常数与动力学和热力学参数之间的关系。观察到的动力学反映了