Quantum Chemical Interpretation of Oxidation Number with Ab Initio Molecular Orbital Wave Functions

Abstract

To interprete the classical concept of the oxidation number accurate electron number analysis around the specified atom in molecules was performed with ab initio molecular orbital wave functions. The studied atomic species are H, C, N, O, F, P, S, and CI. The series of the tetrahedral ions, XO^n- (X=Si, P, S, Cl, Ar), were also studied. The atom difference spherically averaged electron density, Δ_ρo(R) =_ρo(R) _??_ _ρoi (R), on a sphere with radius R centered at the atom concerned, was calculated with various quality of basis sets. There is no dramatic change in the electron number around a specified atom as the classical oxidation number predicts, but a subtle and stepwise change in the Δ_ρo(R) can be detected in parallel with the classical oxidation number. This is the case with not only the inorganic but also organic compounds. It was shown that for less ionic C-H, P-H, N-H, and N-Q bonds the classical assignment of the oxidation number should be a little modified as follows to get the consistency between this electron number analysis and the classical concept.
C-H⁺¹ → C-H^+0.5 ; P-H^+I → P-H⁰
N-H⁺¹ → N-H^0.5 ; N-O^-II → N-0^-1