Charge transfer hydrogen abstraction

Huntress and Elleman 125) have investigated the ion-molecule reactions of N(H,D)3-C(H,D)4 mixtures. They observed proton transfer charge transfer, hydrogen abstraction, and one condensation reaction... 

One aspect of asymmetric catalysis has become clear. Every part of the molecule seems to fulfill a role in the process, just as in enzymic catalysis. Whereas many of us have been used to simple acid or base catalysis, in which protonation or proton abstraction is the key step, bifunctional or even multifunctional catalysis is the rule in the processes discussed in this chapter.Thus it is not only the increase in nucleophilicity of the nucleophile by the quinine base (see Figures 6 and 19), nor only the increase in the electrophilicity of the electrophile caused by hydrogen bonding to the secondary alcohol function of the quinine, but also the many steric (i.e., van der Waals) interactions between the quinoline and quinuclidine portions of the molecule that exert the overall powerful guidance needed to effect high stereoselection. Important charge-transfer interactions between the quinoline portion of the molecule and aromatic substrates cannot be excluded. 

Secondly, instead of a pure and simple electron transfer, the redox reaction can be coupled to a chemical reaction in such a way that the electron transfer takes place either after incorporation of the substrate or an intermediate into the inner coordination sphere of a metal ion ( inner-sphere electron transfer), by formation of a charge transfer complex, or in form of a hydrogen or hydride atom abstraction, respectively. In these cases the reaction between redox catalyst and substrate does not directly depend on the difference of the two standard potentials (see Sect. 2.3). 

In this case, the ethylamine radical is formed by hydrogen abstraction from the solvent, instead of dissociation of the excited (charge-transfer) state of the amide ion pair. 

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