1.2- Elimination reactions, characteristics carbocations

The reactions of copper salts with diacyl peroxides have been investigated quite thoroughly, and the mechanistic studies indicate that both radicals and carbocations are involved as intermediates. The radicals are oxidized to carbocations by Cu(II), and the final products can be recognized as having arisen from carbocations because characteristic patterns of substitution, elimination, and rearrangement can be discerned " ... 

The product of a elimination is a neutral species that resembles a carbocation in having only six carbon valence electrons. The simplest carbene is CH2, methylene. Carbenes are highly reactive, so much so that they cannot be isolated. Their involvement in reactions usually has to be inferred from the nature of the products or the reaction kinetics. The characteristic carbene reactions involve forming an electron-pair bond to the carbene carbon by reacting with cr bonds, it bonds, or unshared pairs ( ), Some of these reactions are illustrated here for methylene ( CH2). ... 

As noted above, most kinetic studies of alkene radical cations in solution have focused on aryl-substituted systems since they have convenient optical propenies and have been extensively studied by other techniques. Radical cations are frequently identified on the basis of their characteristic UV-visible absorptions and the comparison of their spectra to those obtained in matrices at low temperature." However, a number of other diagnostic tests are also commonly employed to identify these intermediates. For example, their kinetic behavior as a function of solvent nucleophilicity or added nucleophiles is analogous to that of other electrophilic species. Thus, reaction with nucleophiles such as azide and halide ions provides support for the assignment of a transient to a radical cation, although it will not serve to eliminate a carbocation intermediate. More useful in the latter respect is the method of generation of the transient since PET does not in general lead to the formation of carbocations. Quenching of the observed transient with a more easily oxidized... 

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