σ-bond conjugation in polysilanes,a pes scaled free-electron approach for the interpretation of skeletal cleavage reactions

The σ-orbital energies calculated by the simple free-electron model with a parametrization procedure proposed recently by Von Szentplay correlate very closely with the σ-band positions of the corresponding photoelectron spectra. For the σ-orbitals of three series of molecules: H(CH₂)_nH (n = 2–4); H(SiH₂)_nH (n = 2–5); Me(SiMe₂)_nMe (n = 2–4) the FEMO model yields a standard error SE) of 0.060 eV. Compared with HMO results (LCGO, LCBO and Sandorfy C) the correlation is significantly improved. The free-electron results are more accurate than those obtained using the PPP, CNDO/2, MINDO/3, SAMO and ab initio methods.The free-electron frontier orbital densities were successfully used to account for features of the skeletal cleavage reactions of polysilanes.