Kinetic and Thermodynamic Acidities of Substituted 1-Benzyl-1-methoxy-2-nitroethylenes. Strong Reduction of the Transition State Imbalance Compared to Other Nitroalkanes
作者:Claude F. Bernasconi、Mahammad Ali、Janette C. Gunter
DOI:10.1021/ja0211398
日期:2003.1.1
Acidity constants of six substituted 1-benzyl-1-methoxy-2-nitroethylenes (2-Z with Z = m-NO(2), m-CF(3), m-Cl, H, p-Me, p-MeO) and their respective nitronic acids were determined in 50% DMSO-50% water (v/v) at 20 degrees C. Kinetic data were obtained on the reversible deprotonation of all six 2-Z by OH(-) and piperidine and on the reversible deprotonation of 2-NO(2)() by piperazine, 1-(2-hydroxyethyl)piperazine
六个取代的 1-苄基-1-甲氧基-2-硝基乙烯(2-Z 与 Z = m-NO(2)、m-CF(3)、m-Cl、H、p-Me、p-MeO)的酸度常数) 及其各自的硝基酸在 20 摄氏度的 50% DMSO-50% 水 (v/v) 中测定。获得了所有六个 2-Z 由 OH(-) 和哌啶可逆去质子化的动力学数据,以及哌嗪、1-(2-羟乙基)哌嗪和吗啉在同一溶剂中对 2-NO(2)() 进行可逆去质子化。这些数据可以确定 Brønsted 系数 alpha(取决于 2-Z 的酸度)和 beta(取决于胺碱度)。α > β 的事实表明存在过渡态不平衡,然而,这比芳基硝基甲烷的去质子化要小得多。