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Reactions of carbocations with carbanions through coordination and single electron transfer. Heterolysis and homolysis of carbon‐carbon bonds

1988; Wiley; Volume: 13-14; Issue: 1 Linguagem: Inglês

10.1002/masy.19880130104

0258-0322

Edward M. Arnett, L. G. Whitesell, Kapil Amarnath, Jin‐Pei Cheng, Etienne Marchot,

Organic Chemistry Cycloaddition Reactions

Abstract Carbocations, carbanions and free radicals are the most important reactive intermediates in organic chemistry and the majority of bond‐forming and bond‐breaking reactions involve their participation at some stage. We will review briefly our studies, over the past five years, of the direct coordination reaction between carbocations and carbanions to form covalent bonds in solution. We have gathered considerable thermodynamic and kinetic information for this reaction. Particular emphasis will be placed on recent work on the measurement and analysis of heterolysis energies. Heterolysis is the reverse of the coordination reaction and we have obtained heterolysis energies in solution for over 160 bonds by measuring the heats of reaction between several resonance‐stabilized carbocations and a variety of carbanions, oxyanions, nitranions a thiophenoxide ions in solution. The results are correlated by very simple equations so that heats of heterolysis may be predicted with considerable precision from readily available data. Carbocations and carbanions can also react by electron transfer to form free radicals. We will describe recent experiments which demonstrate that under appropriate conditions all three types of reactive intermediates can coexist at equilibrium in solution with the electrons shuttling between the three different species.