Semi-empirical MNDO SCF-MO study of radicals derived from γ-radiolysis of tertiary phosphines and trialkylphosphites

Abstract

Calculations have been made, using the MNDO-UHF approximation, of the molecular and electronic structures of a range of phosphorus- and carbon-centred radicals formed in the γ-radiolysis of tertiary phosphines and of trialkylphosphites. The radical cations R₃P⁺ are all calculated to have C_3v, symmetry (for R = Me, Et, Prⁿ, Buⁿ): as the length of the alkyl chain increases, the phosphorus approaches more closely to planarity. In the radical cations (RO)₃P⁺(R = H, Me, Et), the geometry at phosphorus is close to tetrahedral: two conformers, of C₃ and C_s symmetry, were found for (MeO)₃P⁺. Dinuclear cation radicals(R₃P)₂⁺ and [(RO)₃P]₂⁺ were found to be σ* radicals, having the SOMO strongly confined in the P–P bonds. (H₃P)₂⁺ and (Me₃P)₂⁺ are calculated to have D_3d symmetry: for (Et₃P)₂⁺, [(HO)₃P]₂⁺, and [(MeO)₃P]₂⁺ two diastereoisomeric conformers, having D₃ and S₆ symmetry, were found.