Z Dependence of Coupling Constants between Directly Bonded Nuclei. The Value of J (73Ge–13C)

Abstract
The Fermi contact contribution to the reduced, nuclear spin—spin coupling constant of directly bonded atoms, KXN, has been studied by determining the Z dependence of the electron spin density at the nuclei of the isolated atoms. Two methods of calculating the spin density from atomic spectra were tested and the results are employed to determine KXN. It is concluded that KXN for a series of isoelectronic, isostructural compounds varies as κZX, where κ is a relativistic correction which ranges from 1.0 to about 2.5 depending on ZX. The theoretical results are compared with experimental data for symmetrical compounds with bonds of the type XF, XH, and XC, and apparent core polarization contributions to KXN are noted. The directly bonded coupling constant between 73Ge and 13C has been measured in tetramethylgermane; it is 18.7 ± 0.9 Hz.