The structure of 1,2,3,3-tetrachloro-4,5-dimethyl spiro-[2.3] -hexa-1,4-diene

An electron diffraction study of 1,2,3,3-tetrachloro-4,5-dimethyl spiro2.3]-hexa-1,4-diene (Spiro) in the gas phase, confirmed the atom connectivities and led to a structure with roughly tetrahedral bonding about the spiro-carbon atom. The internuclear distances were obtained with moderate precision. The optimum least squares fitting of the experimental molecular scattering function gave a model with C_s symmetry. The r_g values are: (C₃-C₆) = 1.54 (.10) Å (assumed), (C₂-C₃) = 1.52 (.02) Å, <CC >_av= 1.35, (.010) Å, (C₅-C₆) = 1.46 (.02) Å, (C₄-C₇) = 1.52 (.03) Å, (C-Cl) = 1.69 (.03) Å and (-C-Cl) = 1.77 (.03) Å. The angle (θ) between the C₃-C₆ bond and the cyclopropene plane is 127.5°. The large value for <CC >_av is compared with the X-ray crystal structure result, and with the structures of other cyclopropenes and cyclobutenes.