Analysis of One-Bond Se-Se Nuclear Couplings in Diselenides and 1,2-Diselenoles on the Basis of Molecular Orbital Theory: Torsional Angular Dependence, Electron Density Influence, and Origin inJ1(Se, Se)

Abstract

Nuclear couplings for the Se-Se bonds,J1(Se, Se), are analyzed on the basis of the molecular orbital (MO) theory. The values are calculated by employing the tripleζbasis sets of the Slater type at the DFT level.J1(Se, Se)are calculated modeled by MeSeSeMe (1a), which shows the typical torsional angular dependence onϕ(CMeSeSeCMe). The dependence explains well the observedJ1(Se, Se)obsdof small values (≤64 Hz) forRSeSeR′(1) (simple derivatives of1a) and large values (330–380 Hz) observed for 4-substituted naphto[1,8-c,d]-1,2-diselenoles (2) which correspond tosymperiplanardiselenides.J1(Se, Se :2) becomes larger as the electron density on Se increases. The paramagnetic spin-orbit terms contribute predominantly. The contributions are evaluated separately from each MO(ψi)and eachψi→ψatransition, whereψiandψaare occupied and unoccupied MO's, respectively. The separate evaluation enables us to recognize and visualize the origin and the mechanism of the couplings.