Calculation of the n.m.r. spin-spin coupling constants in ethylene

Abstract

A comparison is made of several semi-empirical and non-empirical methods of calculating spin-spin coupling constants. It is concluded that semi-empirical methods are inadequate for accurate calculations, and qualitative and quantitative arguments are given in support of the view that it is essential to allow for electron correlation. A self-consistent-field calculation with configuration interaction gives good agreement with experiment for J cis and J trans in ethylene; the agreement for J gem is less satisfactory, but analysis of the main contribution to J gem shows that it is extremely sensitive to the detailed form of the wave-function.