The influence of spatial orientation of free orbitals in pmr spectroscopy influence of vicinal orbitals on³J and²J

Abstract

Abstract In accordance with recent literature data, it is proposed that an increment of + 2.3 cps and + 1.8 cps is to be added to the vicinal ( 3 J) and gem ( 2 J) coupling values respectively, each time an α‐oxygen (or α‐nitrogen) atom has one of its free electron pair p ‐orbitals parallel with the carbon hydrogen bond of one of the protons involved in the coupling under consideration. An influence on 3 J coupling values in three membered rings (epoxides) is however not to be considered. Molecular deformations which disturb the parallelity (i.e. in the rigid half chair form of pentacyclic compounds or in the twist form of hexacyclic compounds) nullify this effect. The Karplus rule and the electronegativity rule have regained a great amount of their reliability with this supplementary effect.