Carbanions and Electrophilic Aliphatic Substitution

This Chapter Contains Sections titled: Carbanion Structure and Stability Carbanion Reactions Enolates and Related Species Heteroatom-Stabilized Species Organometallic Species Organolithium Species (a) Directed lithiation (b) Addition and other reactions Organomagnesium Species Organozinc Species Other Organometallic Species Miscellaneous Electrophilic Aliphatic Substitution References Contributions by resonance and inductive effects towards the net activation barrier have been determined computationally for the gas-phase SN2 reaction between the acetaldehyde enolate anion and methyl fluoride, for both O-methylation and C-methylation, in order to understand why this reaction favours O-methylation. Mass spectra have been recorded for the gas-phase reactions of cyanomethyl, acetonyl, and (ethoxycarbonyl)methyl carbanions with methyl thiocyanate. A variety of product ions were formed via different reaction mechanisms, depending on the structure and proton affinity of the carbanion. The following pathways have been considered: bimolecular nucleophilic substitution, cyanophilic reaction, thiophilic reaction, and proton transfer, followed in some instances by subsequent transformations. The proposed reaction pathways are supported by density functional theory calculations. A new parameter, trifluoromethylthio cation-donating ability, has been introduced as a quantitative descriptor for the propensity of electrophilic trifluoromethylthiolating reagents to transfer a CF3S moiety in organic synthesis.