The designation of E/Z-geometrical isomers in 3-acylidene 2-oxindoles by NMR spectroscopy can lead to erroneous assignment of alkene stereochemistry because of the narrow chemical shift range observed over a large series of analogues. In contrast, UV-Vis spectroscopy offers a convenient and more reliable method for alkene stereochemical assignment. A combination of X-ray crystallography and theoretical studies shows that the observed differences in UV-Vis spectroscopic behaviour relate to the twisted conformation of the Z-isomers that provides reduced conjugation and weaker hypsochromic (blue-shifted) absorbances relative to those of the E-isomers.
通过NMR光谱对3-酰基
吲哚类化合物中E/Z几何异构体的命名可能会导致不正确的烯烃立体
化学分配,因为在一系列大类类似物中观察到的
化学位移范围较窄。相较之下,UV-Vis光谱为烯烃立体
化学分配提供了一种方便且更可靠的方法。X射线晶体学与理论研究的结合表明,UV-Vis光谱行为的观察差异与Z-异构体的扭曲构象有关,该构象相对于E-异构体提供了降低的共轭效应和较弱的紫外光移吸收。