关于核磁共振中ABX体系的各种跃迁与体系耦合常数符号之间的关系

THE RELATIONSHIP BETWEEN THE POSITIONS OF EACH TRANSITION IN ABX SYSTEM AND THEIR RELATIVE SIGNS OF COUPLING CONSTANTS IN NMR

本文用ABC体系理论分析了ABX体系各特定跃迁的位置与强度,弄清它们与耦合常数之大小及其符号的一般变化规律,从而沟通了实测谱图与能级关联图、能级简图及耦合常数符号之间的关系.提出了只对体系作出初略强度分析以及通过双共振方法可容易地判断体系的耦合常数的相对符号的方法.

According to the theory of ABC system, theoretical spectra of ABX system were calculated by varying |J| < 16Hz and the positions and intensities of each specific transitions were analyzed The general rules of the position of each transition in ABX system with various values of coupling constants and their signs were found out Then, a simple procedure was designed by which relative signs of couping constants can be obtained without calculating precisely through intensities of each peak, as follows: 1. To distinguish the four peaks of each A, B, X nuclei in ABX system and to give their marks in order, respectively. (For example, from left to right, a1 ~ a4,b1 ~ b4,and x1 ~ x4, neglecting the mixing transitions. ) 1 To get a related diagram discribing the relationship between each peak using double resonance methods. 3. Through inter-exchanging of the marks of the same kind of peaks, finally you can always let a1, b1, x1 to be at the bottom and a4, b4, x4 on the top as a usual diagram of energy level. 4. If you don't need to inter - exchange any marks of peaks, the signs of three coupling constants are the same; if you need to do, then, the sign of coupling constant between relative nuclei due to inter-exchanging must be opposite sign to the other two.