Secondary steric effects in SNAr of thiophenes: a coordinate kinetic, thermodynamic, UV–VIS, crystallographic and ab initio study
作者:Giovanni Consiglio、Vincenzo Frenna、Angelo Mugnoli、Renato Noto、Marcella Pani、Domenico Spinelli
DOI:10.1039/a604516b
日期:——
The reactivity of some dinitro-benzene and -thiophene derivatives
with piperidine and sodium benzenethiolate has been examined giving
evidence that benzenes show large and thiophenes show small kinetic
secondary steric effects, respectively. The acid dissociation reaction
and the UVâVIS spectra of some nitrothiophenamines have also been
studied. The crystal structure and the absolute conformation of
2-iodo-3,5-dinitrothiophene and of 2-iodo-4-methyl-3,5-dinitrothiophene
have been determined. For different conformations of the analogous
chlorodinitro derivatives in the thiophene and benzene series, ab
initio energy calculations have been performed. The results
collected show that steric strain among adjacent groups affects the
benzene and thiophene compounds and the kinetic, thermodynamic and
spectroscopic properties of the molecules examined differently.
Differences in geometry of the two aromatic rings and then in rotation
of nitro groups with respect to the rings themselves as well as
differences along reaction coordinates (essentially depending on
hybridation changes) are used to explain the above data.
一些二硝基苯和二硫吡啶衍生物与哌啶和苯硫醇钠的反应性已被研究,结果表明苯类化合物显示出较大的动力学次级空间效应,而噻吩类化合物则显示出较小的动力学次级空间效应。还研究了一些硝基噻吡啶胺的酸解离反应及其紫外-可见光谱。已确定了2-碘-3,5-二硝基噻吡啶和2-碘-4-甲基-3,5-二硝基噻吡啶的晶体结构与绝对构象。对于硫代吡啶和苯系列中类似氯代二硝基衍生物的不同构象,进行了从头算能量计算。收集的结果表明,相邻基团之间的立体应变对苯和噻吡啶化合物的影响,以及所研究分子的动力学、热力学和光谱特性不同。两种芳香环的几何结构差异,以及相对于环本身的硝基旋转差异,以及沿反应坐标的差异(主要依赖于杂化变化)被用来解释上述数据。