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in 3b and 3c are in the vicinity of 0.4 e. An estimate of the relative capabilities of the 0, C(CN&, and tetrachlorocyclopentadienylidene groups for - charge stabilization, in PROPEN, CYANOF, and the tetrachloropentatriafulvalenes, can be obtained from the acidities of the conjugate acids HzO, H2C(CN),, and 1,2,3,4-tetrachlorocyclopentadiene. Although the pK, of the latter compound is not presently known, the similarities of the pK,’s of water (14) and malononitrile (1 1. 144?), and the similarities between the three-ring bond distance in the cyclopropenone and the three fulvenes, wggest that the pK, of the tetrachlorocyclopentadiene would be in the 11-14 range, Further attempts to induce even larger amounts of charge separation than the ca. 4 0 z found in CYANOF and PROPEN should consider CH2X2 compounds which (42) I
