Conformational equilibria and torsional barriers of the isopropyl groups inN,N-diiso-propylbenzamide and its thio and seleno analogues
作者:Ulf Berg、Ingrid Pettersson
DOI:10.1002/mrc.1260230711
日期:1985.7
The conformations of the isopropyl groups and the barriers to conformational interconversion in N,N-diiso-propylbenzamide (1), and its thio (2) and seleno (3) analogues have been studied by dynamic 1H NMR spectroscopy. In 1 only one conformation is observed, whereas 2 and 3 exist as mixtures of three conformations. The use of the strongly deshielding CX (X = O, S, Se) group and comparison with earlier results on similar systems allows total assignment, in the case of 2, rectifying an earlier proposal. The temperature dependence of the NMR spectra of 2 and 3 clearly shows that the E- and Z-isopropyl groups rotate with very different rates, thus providing experimental evidence for the stepwise nature of the conformational interchange.
通过动态 1H NMR 光谱法研究了 N,N-二异丙基苯甲酰胺(1)及其硫代(2)和硒代(3)类似物中异丙基的构象和构象相互转换的障碍。在 1 中只观察到一种构象,而 2 和 3 则存在三种构象的混合物。通过使用强去屏蔽的 CX (X = O、S、Se)基团,并与之前对类似体系的研究结果进行比较,可以完全确定 2 的构象,从而纠正了之前的提议。2 和 3 的核磁共振光谱与温度的关系清楚地表明,E-异丙基和 Z-异丙基旋转的速度非常不同,从而为构象互换的逐步性质提供了实验证据。