regions of the molecule; around the benzo moiety and the phenyl group at C5. Separation of the disordered structures was not straightforward since several of the related disordered atoms were located within 0.5 Á of each other. Nonetheless, smooth convergence was eventually realized by constraining corresponding bond lengths to be equal within = 0.005 Á. The phenyl groups were treated as rigid planar groups with C-C bond lengths 1.395 A and internal angle 120°. Only the hydrogen atoms around the nondisordered phenyl group at Cl, which could be readily located on a difference Fourier map, were included in the refinement with fixed coordinates and temperature factors. The occupancy factors of the disordered structures, constrained to add to 1.0, refined to 50% in each region. This value was fixed in the final stages of structural refinement. A unit weighting scheme was found to be adequate.When all the non-hydrogen atoms in the disordered structure were refined with individual temperature factors, the conventional R factor converged to 0.105. Further structural refinement with anisotropic temperature factors for the atoms of the ozonide ring and the phenyl group at Cl, which were not evidently disordered, produced an R factor of 0.092. The final difference Fourier map contained no feature greater than ±0.36 e" A"3.In addition to the tabulated material already mentioned in the main text, tables of thermal vibrational parameters, calculated least-square planes, and observed and calculated structure factor amplitudes for each determination are available as supplementary material.University) for use of computer programs, and the University of Aberdeen Computer Centre for computer time.
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