Molecular Structures of Gaseous Hexabromo- and ortho-Dibromobenzene as Determined by Electron Diffraction

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Abstract
The molecular structures of hexabromo‐ and ortho‐dibromobenzene have been studied by least‐squares refinements based on gaseous electron‐diffraction intensity data. The equilibrium conformation of ortho‐dibromobenzene is found to be planar with C2v symmetry and with an angle of 63.6°±0.5° between the two carbon—bromine bonds. For hexabromobenzene, the ortho‐bromine—bromine distance indicates a distorted structure possessing S6 symmetry with every second bromine atom above and below the plane of the benzene ring. The other bromine—bromine and the nonbonded carbon—bromine distances, however, are in better agreement with a planar and undistorted configuration. Possible structures of this molecule are discussed in the text. The most important molecular parameters and estimated standard deviations are listed in Table IV. Accurate partial‐wave scattering factors for the atomic scattering of 40‐keV electrons have been applied in some refinements. The results are compared with the results obtained using scattering factors according to the first Born approximation, and a better agreement with the experimental data is observed for the former scattering factors.