Calculations of N.M.R. spin-spin coupling constants of fluoromethanes and other first-row fluorides

Abstract

Calculations of the coupling constants in the fluoromethanes and other first-row fluorides are reported. The theoretical basis is the one electron valence shell MO theory of Pople and Santry. Coulomb integrals were taken as Skinner-Pritchard valence state ionization potential values, corrected for drift of electrons from less electronegative to more electronegative atoms. The amount of correction was estimated from trial calculations on BF₃. Calculations on F₂ showed that it was necessary to use the Mulliken approximation for estimating resonance integrals. The effect of varying the scale factor in the Mulliken approximation was examined, as was the effect of varying the Slater exponent of hydrogen. Best agreement with experimental bonded coupling constants came from a scale factor of 0·75 and a hydrogen Slater exponent of 1·3. Calculated geminal couplings were in poor agreement with experiment.