Nonlinear Hammett plots in pyridinolysis of 2,4-dinitrophenyl X-substituted benzoates: change in RDS versus resonance contribution
作者:Ik-Hwan Um、Li-Ra Im、Eun-Hee Kim、Ji Hye Shin
DOI:10.1039/c0ob00031k
日期:——
Second-order rate constants (kOH–) have been measured for nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzoates (1a–j) with Z-substituted pyridines in 80 mol% H2O/20 mol% DMSO at 25.0 ± 0.1 °C. The Hammett plots for the reactions of 1a–j with pyridines consist of two intersecting straight lines, i.e., a large ρ value for the reactions of substrates (1a–c) possessing an electron-donating
在80 mol%H 2 O / 20 mol%中,已测量了2,4-二硝基苯基X-取代的苯甲酸酯(1a–j)与Z-取代的吡啶的亲核取代反应的二级速率常数(k OH –)。二甲基亚砜在25.0±0.1°C下。1a–j与吡啶反应的哈米特图由两条相交的直线组成,即具有给电子基团的底物(1a–c)的反应的大ρ值(EDG)中的苯甲酰基部分和一小部分用于带有吸电子基团(EWG)的底物(1e–j)。非线性的哈米特图被归因于通过给电子取代基和羰基官能团之间的共振相互作用,使底物1a-c的基态稳定,因为相应的汤川-特苏诺图显示了具有大r值的出色线性相关性。研究表明,底物1e–j的反应活性并不比Hammett取代基常数所预期的要高,而底物1a–c的反应性却比预期的要低。1a–j吡啶分解的布朗斯台德型图是直链与β NUC = 0.74-0.98,表明通过逐步机制反应的进行,其中第二步是RDS。已经得出的结论是,苯