Stable overcrowded ethylene dianions, viz. bifluoren-9-ylidene dianion (1 )2-and bi-(4H-cyclopenta[defjphenanthren-4-ylidene) dianion (2)*-were prepared via metal reduction and characterized by 1H and 13C n.m.r. spectroscopy; the spectroscopic results as well as cop calculations performed on the hydrocarbons (1) and (2) and the corresponding dianions (1)*-and (2)2-are discussed with respect to their diatropicity and spatial structure.Bifluoren-9-ylidene (1) is a classical example of the family of the highly strained overcrowded ethylenes which have attracted chemists' attention in the last forty years.I.2 The introduction of dynamic n.m.r. spectroscopy as well as other modern class of compounds in s0lution3.~ as well as in the solid state to
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