EFFECT OF HYDROGENS IN BETA-POSITION UPON THE VICINAL COUPLINGS (3)J(HH) AN AB-INITIO STUDY

Equations for describing the effect of hydrogens in beta position (bet a effect) over the vicinal proton-proton coupling constants, (3)J(HH), formulated. These equations were applied to a dataset of (3)J(HH) val ues calculated by SCF ab initio (levels STO-SG and 6-31G*) and semiem pirical (INDO/FPT) methods for monosubstituted ethanes with substituen ts CH3, NH2 and OH. The Fermi contact interaction is the most importan t one to describe the beta effect, being the remaining interactions ne gligible. The three used methods of calculation provide similar result s. However, the beta effect complexity increases with the calculation quality. The results show a complicated beta effect whose precise desc ription requires to take at least eleven terms in the equations.