AM1 AND SINGLE-CRYSTAL X-RAY-DIFFRACTION STUDY OF THE CONFORMATIONAL PROPERTIES OF CHLORINATED DIPHENYL ETHERS

Structural and conformational properties of 11 polychlorinated dipheny l ethers (PCDEs) 1-11 and thyroxine derivative 12 were studied by the semiempirical AM1 method. In addition, the molecular structures of six PCDEs 1-6 were solved by X-ray crystallography. Conformational analys es for diphenyl ethers 1-12 were performed and the resulting conformat ional energy maps obtained. The calculated energy minima of PCDEs were obtained, and the structural parameters were compared with the X-ray structures. The X-ray-determined geometries were found to be inside th e low-energy regions close to the global energy minima except for comp ound 2, whose X-ray structure deviates considerably from the global mi nima. The X-ray structures of PCDE were non-planar, with dihedral angl es between two benzene rings ranging from 59.0 degrees to 99.7 degrees .