VITAMIN-B6 MODEL REACTIONS .6. A HAMMETT RELATIONSHIP FOR THE MAGNITUDE OF PSEUDOALLYLIC PROTON-PROTON SPIN COUPLING-CONSTANTS IN SUBSTITUTED AZOMETHINES

Four-bond proton-proton spin coupling constants were measured between the azomethine proton and the glycine CH protons of some coordinated g lycine Schiff bases where the parent aldehyde is aromatic, Such system s are models for vitamin B-6 enzyme substrate complexes, It is demonst rated that the coupling constants are not only related to the dihedral angles between coupled systems but they are also linearly related to the Hammett sigma value of the substituents on the aromatic ring. A me thod is suggested for the calculation of dihedral angles between proto n-carbon bonds in these pseudoallylic systems.