Perchlorinated organic radicals and related intermediates

Front-strain between its two perchlorobenzyl moieties causes dissociation of the dimer (PB)2 to PB-. The minimal distance between two chlorine nuclei in a molecule is about 3.0 A, but in the planar conformation of PB- the distance between an o-chlorine and an a-chlorine would be about 2.5 A (see Fig. 10). Consequently, to relieve the relevant steric strain, the plane of the dichloromethylene must rotate with respect to that of the pentachlorophenyl (p. 428). 

The remarkable chemical stability of PB- is thus mainly due to steric compression in the would-be transition states and/or products. Nevertheless, PB- reacts immediately with comparatively small molecules, such as oxygen, and hydrogen-atom donors like toluene (p. 383). 

The radical p—CCI3—C6CI4—CC 2 (CCI3—PB ) has been detected as an intermediate in reductive polymerization of perchloro-p-xylene, giving the polymeric chlorocarbon PP-xynene (p. 304) (Doorenbos, 1969). 

An alternative, high-yield synthesis of PDM- starts from a nonstrained, readily accessible precursor, a//-undecachlorodiphenylmethane (Ballester et al., 1971d). Because of the cumulative inductive effect of its chlorines, the latter is converted into perchlorodiphenylmethyl anion (PDM ) with hydroxide ion in DMSO/ether solutions. PDM is oxidized with iodine to give a nearly quantitative yield of PDM- (126). 

PDM- is completely dissociated, even in solid form. The purity of this and related radicals considered here has been ascertained by magnetic-susceptibility measurements, giving values near 6 x 10 spin mol i.e. about 100% purity. Nevertheless, in solution, at room temperature, PDM- withstands bromine, chlorine, concentrated nitric acid, and other aggressive chemical species. In solution, it decomposes slowly in air giving mainly perchloroben-zophenone, with a half-life of 2-3 days. 

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Thermal dimerization of 2,3,5,6-tetrachloro-p-phenylenediimine 351 A remarkable benzidine rearrangement 352 Condensation of aromatic perchloroamines 353 Perchlorinated organic radicals and related intermediates 354 Perchlorobenzyl radicals 354 Perchlorodiphenylmethyl radicals 355 Perchlorotriphenylmethyi radicals 361 Perchloro-9-phenylfluorenyl radicals and related species 384 Inert perchloro-aza-radicals 389 Perchloro-p-quinodimethanes, perchloro-/ -xylylenes and related compounds 390... 

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