The Geometry of Carbanions

The stable carbanions may belong in a special category since their stability is in most cases due to resonance, and the resonance has geometrical requirements that might or might not be the same as those of the bond hybridization of an ordinary carbanion. The central hydrogen of triptycene has none of the acidity of the central hydrogen of triphenylmethane.364 

All things considered, the best a priori guess would be that carbanions of any degree of stability will be incapable of retaining optical asymmetry but capable of retaining a cis or trans configuration at a double bond. Neither expectation is contradicted by the available facts. 

Early reports of the persistance of optical activity in nitro-substituted carbanions have since been shown to be erroneous.365 366 The treatment of optically active 2-nitrooctane with sodium ethoxide or hydroxide produces an optically inactive salt.366 Optically active 4-nitropentanoic acid racemizes and enolizes at the same rate in the presence of a base.368 Optically active phenyl sec-butyl ketone racemizes and undergoes deuterium exchange at the same rate in the presence of DQ -)a 7 Of course this could conceivably be due to the tendency of the 

The only currently unrefuted evidence even suggestive of an optically active carbanion is the report of optically active 2-octyl-lithium.899 It should be recalled, however, that ordinary alkyl lithium compounds are volatile, soluble in non-polar solvents, and generally more covalent than ionic in their behavior. 

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