Importance of Multicenter Integrals in Semiempirical Calculations of Nuclear Spin-Spin Coupling Constants. 1. Isotropic Coupling

A study of Fermi contact, orbital, and spin-dipolar contributions to isotropic nuclear spin-spin coupling constants is presented in terms of a semiempirical (INDO) molecular orbital (MO) approach that extends existing theory to include all integrals for the three types of terms over Slater-type orbitals (STO's). All contributions are evaluated by the first-order polarization propagator approach (FOPPA), which is equivalent to the coupled Hartree-Fock (CHF) theory. Calculated coupling constant results for representative molecules are compared with experimental data, and reasonable correspondence is noted between these noncontact contributions and ab initio results with large Gaussian basis sets. Detailed comparisons are also made with semiempirical SCPT-MO results in the one-center integral approximation. Since the latter procedure leads to identically zero orbital and dipolar contributions if either one of the coupled nuclei is a proton, this extension of the theory is applicable to many very important types of coupling. For example, the calculated geminal and vicinal ¹H-¹⁹F coupling constants, for which the OB and SD contributions are important, are in better conformity with the experimental data. It is now clear that the scaling of the one-center integrals for carbon far above the atomic Hartree-Fock values may be a consequence of the neglect of the multicenter integrals. The introduction of multicenter integrals into semiempirical methods greatly extends the number and the complexity of molecules for which contributions of all mechanisms can be investigated. © 1984, American Chemical Society. All rights reserved.

Duke Scholars

Author Julio Cesar Facelli Biostatistics & Bioinformatics, Division of Translational Bi ...