ABINITIO QUADRATIC CONFIGURATION-INTERACTION CALCULATION OF INDIRECT NMR SPIN-SPIN COUPLING-CONSTANTS

Finite-field perturbation theory is combined with the quadratic configuration interaction method of ab initio electronic structure theory to calculate the Fermi-contact component of the indirect spin-spin coupling constant between adjacent carbon nuclei in a range of bonding environments. Basis set requirements for accuracy are first investigated in ethane and a small modification of the outer-core, inner-valence region of the standard Dunning double-zeta contraction is shown to be satisfactory. Calculations with this basis set then allow the accurate determination of the contact component of 1J(C-13C-13) in ethane, (34.1 Hz), cyclopropane, (13.9 Hz), cyclobutane, (27.4 Hz), and bicyclo[1.1.0] butane, (24.3 Hz), including a prediction (-13.6 Hz) of the coupling across the central bridge in this latter system.