Structure and inversion potential of thianthren

Abstract

A least squares reduction of the scattered intensity pattern, pM(p), [p(60/λ) sin θ/2], of thianthren assuming C_2v symmetry, undistorted benzene rings and planar C₆H₄S₂ groups gave the following r_g values: 〈C—C〉= 1.400(2)Å, (C—S)= 1.770(3)Å, (C—H)= 1.082(22)Å, θ(dihedral angle)= 131.4(3)° with σ= 0.029 0. Models with slightly distorted benzene rings or non-planar C₆H₄S₂ groups did not give an improved fit to the diffraction data. Comparisons are presented of the available structural data for thianthren and related molecules.

A complete normal mode analysis was carried out to investigate the inversion and twisting motions of thianthren. It was concluded that the assumption of small harmonic vibrations did not adequately represent these motions. A number of models were tested assuming an inversion barrier of the form A(ϕ⁴–Bϕ²), [ϕ(π–θ)/2]; the best of these gave V₀ 4 kcal mol^–1 for the inversion barrier and θ₀= 128–130° for the dihedral angle at the energy minimum.