Proton Transfers Involving Anions and Dianions

Bam S Correlation Consistent Sets DNA Bases and Base Pairs Ab Initio Calculations Intermolecular Interactions by Perturbation Theory Proton Transfers Involving Anions and Dianions Solvation Modeling Water Clusters,... 

The simplest reaction characteristic of compounds that are regarded as salts of carbanions is that of proton transfer (see Proton Transfers Involving Anions and Dianions) and a number of these have been studied. A typical example is the reaction of methane with lithium amide. This reaction is a model for many known hydrogen isotope exchange reactions of hydrocarbons with lithium and cesium cyclohexylamide whose kinetics have been measured in cyclohexylamine. The model reaction does involve a preliminary weakly bound complex that isomerizes via a transition structure to methyllithium coordinated to ammonia (Figure 3). 

Density Functional Applications G2 Theory M0l-ler-Plesset Perturbation Theory Proton Transfers Involving Anions and Dianions. 

The stereochemical consequences of the methanolyses of the monoanion of phenyl [ 0, 0, 0]phosphate, the dianion of 4-nitrophenyl [" 0, 0, 0] phosphate, and [ 0, 0, 0]phosphocreatine have been determined by Knowles and co-workers (35). The monoanion of phenyl phosphate behaves as a typical phosphate monoester in that its rate of hydrolysis is maximal at pH 4, where an intramolecular proton transfer is possible. The dianion of 4-nitrophenyl phosphate is highly reactive since protonation of the leaving group is not necessary. Finally, A-phosphoguanidines have been reported to be the most reactive phosphoryl compound (the chiral phosphocreatine can be enzymically synthesized from [ y- 0, 0, 0]ATP). Thus, the solvolyses of all three of these compounds are believed to involve the participation of metaphosphate anion. The meth-anolysis of each of these compounds proceeds with quantitative inversion of configuration. 

Table 3 lists a selection of rate constants for proton transfer in DMSO solution, which indicate not only the range of rates involved in common EGB reactions but also that structural features operate in a qualitatively predictable manner. It is safe to conclude from these data that, kinetically, azobenzene radical anion is probably a stronger base than the phenazine radical anion and that the dianions of the 9-fluorenylidine derivatives are relatively weak bases. 

The dissociation (i.e. fragmentation of the Ca—bond) of C-alkylates was proposed to take place in a process involving transfer of two electrons and not through dissociation of radical anions. Thus, the /7-nitrocumene found was suggested to arise from protonation of the corresponding anion, generated by fragmentation of the dianion of the C-alkylates. 

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