maléate (10%, 8% yield). The last two fractions were essentially pure exo ester, bp 123°(22 mm), m24d 1.4675 (lit.37 bp 109-110°( 18 mm)).

Perchloro-organic compounds can be viewed as constituting a chemical domain analogous to that of conventional organic chemistry. To each compound belonging to the latter-and containing at least one hydrogen atom-there can be imagined a corresponding related member belonging to the former as a result of replacing all hydrogens by chlorine atoms (perchlorination).The initiation of this "perchloro-organic" chemistry can be ascribed to the pioneering syntheses, by Faraday and Julin in 1821, of hexachloroethane, tetrachloroethylene, and hexachlorobenzene.1 The field then remained almost dormant for nearly 140 years in spite of numerous

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The syntheses of 1,1',3,3',6,6',8,8'-octachloro-9,9'-bifluorenylidene (1), its precursors, and the byproduct 3,3',5,5'-tetrachloro-4-(trichloromethyl)biphenyl (5) are described. Accurate structural X-ray data on 1 and on perchloro-9,9'-bifluorenylidene (2) are reported and discussed. Because of chlorine overcrowding, the dihedral angles between their two identical fluorenylidene moieties are abnormally large, the central-ethylene twist angles being 55 and 66 degrees, respectively. Significant out-of-plane carbon-chlorine bond bending is likewise exhibited. Their ESR spectra and magnetic measurements prove that they are singlet species. The exceptionally large bathochromic displacements of their UV-vis absorption spectrum with respect to that of their parent hydrocarbon are mainly attributed to bond bending and molecular warping.

Abstract