Carbanions, and stability

More recent developments are based on the finding, that the d-orbitals of silicon, sulfur, phosphorus and certain transition metals may also stabilize a negative charge on a carbon atom. This is probably caused by a partial transfer of electron density from the carbanion into empty low-energy d-orbitals of the hetero atom ( backbonding ) or by the formation of ylides , in which a positively charged onium centre is adjacent to the carbanion and stabilization occurs by ylene formation. 

Introduction of a j8-alkyl substituent should make the reaction more El-like (or less Elcb-like). That is, an Elcb-like reaction should become more synchronous because the alkyl substituent would be expected to destabilize a developing carbanion and stabilize the incipient carbon-carbon double bond. An El-like reaction should become even more El-like. 

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See also in sourсe #XX -- [ , , , , , ]

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