共轭体系的分类及结构特征

Classification and Structural Characteristics of Conjugated System

共轭体系是相邻原子或基团的电子轨道发生重叠,电子发生离域运动、体系能量降低、键长平均化的结构单元,具有独特的电子效应--共轭效应。共轭效应是有机化学课程的重点和难点内容,掌握共轭体系的分类及结构特征,对理解化合物的共轭效应以及物理化学性质具有重要作用。但一般的有机化学教材及文献对此没有系统的介绍。本文通过实例、价键(valence bond, VB)理论以及分子轨道(molecular orbital, MO)理论中的电子轨道示意图,阐明广义和狭义共轭体系的内涵,以及狭义共轭体系、超共轭体系、价键共轭与空间共轭的分类和结构特征。

Conjugated system,the moiety that the electronic orbitals of adjacent atoms or groups overlap,the electrons delocalize and the bond lengths become average,has special electronic effects,i.e.,the conjugate effect that is crucial and difficult in organic chemistry course.It is very important to master the classification and structural characteristics of conjugated systems for understanding the conjugate effect,as well as physical and chemical properties of compounds.However,these have not been systematically discussed in general organic chemistry textbooks and literature.Here,the broad and narrow sense of conjugated systems,the classification and structural characteristics of narrow-sense conjugated system,hyper-conjugated system,through-bond and through-space conjugations were illustrated through the molecular structures of examples and the electronic orbital figures of valence bond and molecular orbital theories.