Electron-Coupled Proton Spin-Spin Interaction in Saturated Hydrocarbon Molecule. I

Electron coupled proton spin-spin interactions in saturated hydrocarbon molecules. J HH' , are investigated theoretically. The general formula for J HH' is derived by double perturbation method, in which \(HF\) (the Fermi interactions between electrons and proton-spins) and \(H₁\) (correlations between electrons) are taken as perturbations. The calculation is performed up to first order in \(H₁\). It is shown that the zeroth order term in \(H₁\) becomes nearly equal to zero under the approximation, in which energy differences between the ground state and the excited states are replaced by a suitable mean. Therefore, J HH' calculated by the molecular orbital method without configuration interactions is a part of J HH' , which is different from the one calculated by the valence bond method with the above approximation. The order of magnitudes of the zeroth and the first order term in \(H₁\) are compared in the case of methane molecule.