γ-旁氏效应及其在立体异构体确定中的应用  

γ-Gauche Effect and Its Application in the Determination of Stereoisomers

作　　者：陈宁 许家喜 CHEN Ning;XU Jia-Xi(Cllege of Chemistry,Beijing University of Chemical Technology,Bejing 100029,China)

机构地区：[1]北京化工大学化学学院,北京100029

出　　处：《化学教育（中英文）》2022年第18期119-124,共6页Chinese Journal of Chemical Education

基　　金：北京化工大学有机化学本科育人团队项目;北京化工大学德智体美劳教学改革研究项目(2021BHDJGYB27);有机化学和中级有机化学一流课程建设项目。

摘　　要：核磁共振碳谱中,碳化学位移受立体结构影响很大。同族原子中,和含相对较小的电负性原子(如Br/I)分子相比,大电负性原子(如F/Cl)会使其相连的α-碳化学位移增大,而β-及γ-碳化学位移更小。多数教材对其解释过于抽象,让学生理解困难。本文通过立体电子效应和位阻效应详细解释了取代基对于β-和γ-碳化学位移的影响。这些影响中,γ-旁氏效应应用最为广泛,常用于确定立体异构体的构型。大电负性原子有助于提高分子中邻位交叉式构象的比例。进而通过空间排斥,使该原子处于γ-位C—H键的电子云移向碳端,导致σ键中的氢原子去屏蔽而碳原子屏蔽,进而该γ-位C—H键中相应氢化学位移增大,而碳化学位移减小。这种空间排斥更多见于固定环体系,从而可广泛用于立体异构体的结构分析中。此外,还分享了部分文献和本课题组的数据,帮助读者更好地将其运用于教学和科研中。InC NMR, the chemical shift of the carbons is greatly affected by the stereostructure. Among the atoms of the same group, compared with molecules containing relatively small electronegative atoms(such as Br/I), large electronegative atoms(such as F/Cl) will increase the chemical shift of the α-carbon to which it is connected, and decrease that of its β-and γ-carbon. Most textbooks are too abstract on their explanation, which makes if difficult for students to understand. This paper explained in detail the influence of substituents on the chemical shifts of β-and γ-carbons through the steric electronic effects and steric hindrance effects. Among these effects, the γ-gauche effect is the most widely used that is often applied for the determination of the configuration of stereoisomers. The large electronegative atom helps to increase the ratio of the gauche conformation of the molecules. Through steric repulsion, the electron cloud of the C—H bond at the γ-position moves to the carbon site, resulting in the deshielding of hydrogen and shielding of carbon in the σ-bond, so that the corresponding hydrogen chemical shift in the γ-position C—H bond increases, while the carbon chemical shift decreases. This kind of spatial repulsion is more valuable in ring systems, which therefore can be widely used for the structural analysis of isomers. In addition, this paper also shares the data from literatures and our group to help readers on their teaching and scientific research.

关 键 词：波谱教学 核磁共振碳谱 γ-旁氏效应 结构鉴定 立体电子效应 

分 类 号：O641.6[理学—物理化学]