Determination of the molecular structure and the internal rotation potential of dichlorophenylphosphine using gas electron diffraction and relaxation constraints from ab initio calculations

Abstract

Gas electron diffraction data are applied to determine the geometrical parameters of the dichlorophenylphosphine molecule using a dynamic model where the rotation of the PCl 2-group was treated as a large amplitude motion. The structural parameters and parameters of the potential function were refined taking into account the relaxation of the molecular geometry estimated from ab initio calculations at the Hartree-Fock level of theory using a 6-31G∗∗ basis set. The internal rotation potential was found to have a unique minimum at ϕ = 0°, where ϕ is an angle between a bisector of the CIPCI angle and the plane of the benzene ring, and the potential has been described as the function V( ϕ) = 0.5 V 2(1 − cos2 ϕ) with V 2 = 1.24 ± 0.54 kcal mol −1. The geometric parameters for the conformer at ϕ = 0° ( r a in Å, ∠ α in degrees and errors given as three times the standard deviations including a scale error) are: r(PCl) = 2.060(3), r(PC) = 1.823(5), r(CC) = 1.396(2), r(CH) = 1.098(9), ∠CPCl = 100.5(5), ∠ClPCl = 100.2(5), ∠CC 1C = 121.2(9), ∠CC 2C = 119.5(8), ∠CC 6C = 119.8(8), ∠ δ = 5.0(5), where δ is an angle between a PC bond and a bisector of the CC 1C angle. The structural parameters are compared with those obtained for related compounds. The steric interactions are shown to have a more important effect on the geometry of the phenylphosphine derivatives than the p- π-conjugation.