DETERMINATION OF THE MOLECULAR-STRUCTURE AND THE INTERNAL-ROTATION POTENTIAL OF DICHLOROPHENYLPHOSPHINE USING GAS ELECTRON-DIFFRACTION AND RELAXATION CONSTRAINTS FROM AB-INITIO CALCULATIONS

Gas electron diffraction data are applied to determine the geometrical parameters of the dichlorophenylphosphine molecule using a dynamic mo del where the rotation of the PCl2-group was treated as a large amplit ude motion. The structural parameters and parameters of the potential function were refined taking into account the relaxation of the molecu lar geometry estimated from ab initio calculations at the Hartree-Fock level of theory using a 6-31G* basis set. The internal rotation pote ntial was found to have a unique minimum at phi = 0 degrees, where phi is an angle between a bisector of the ClPCl angle and the plane of th e benzene ring, and the potential has been described as the function V (phi) = 0.5 V-2(1-cos2 phi) with V-2 = 1.24 +/- 0.54 kcal mol(-1) The geometric parameters for the conformer at phi = 0 degrees (r(a) in Ang strom, angle(c) in degrees and errors given as three times the standar d 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), angle CPCl= 100.5(5), angle ClPCl = 100.2(5), angle CC1C = 121.2(9), angle CC2C = 119.5(8), angle CC6C = 119.8 (8), angle delta = 5.0(5), where delta is an angle between a P-C bond and a bisector of the CC1C angle, The structural p arameters are compared with those obtained for related compounds. The steric interactions are shown to have a more important effect on the g eometry of the phenylphosphine derivatives than the p-pi-conjugation. (C) 1997 Elsevier Science B.V.