The influence of some steric and electron effects on the mechanism of aromatic nucleophilic substitution (SNAr) reactions in nonpolar solvent
作者:Thomas A. Emokpae、Nkechi V. Atasie
DOI:10.1002/kin.20109
日期:2005.12
reported for the reactions with aniline in benzene of a series of X-phenyl 2,4,6-trinitrophenyl ethers [X = H; 2-, 3-, 4-CH3; 2,4-, or 2,6-(CH3)2] a–f, and the results compared with those of the corresponding nitro derivatives. In the methyl series, kinetic data show that increasing substitution reduces drastically the rates of reactions indicative of the operation of some kind of steric effect. The unfavorable
动力学研究报道了一系列 X-苯基 2,4,6-三硝基苯基醚 [X = H; 2-、3-、4-CH3;2,4- 或 2,6-(CH3)2] a-f,并将结果与相应的硝基衍生物的结果进行比较。在甲基系列中,动力学数据表明,增加取代会大大降低反应速率,这表明某种空间效应的作用。反应中心不利的空间拥挤似乎对确定反应的动力学顺序并不重要。通常,二级速率常数 kA 线性依赖于亲核试剂浓度的平方。在硝基衍生物中观察到的动力学形式的变化可能主要是由于该基团的吸电子效应。然而,对于 2,6-二硝基衍生物,未催化的途径 k2 占据了所有的反应通量。分子间质子从碱基转移到中间体的醚氧的空间位阻足以使碱基催化途径相对于k2途径无关紧要。© 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 744–750, 2005