Dications carbenium-carbonium

In addition to the carbenium-carbonium dications (i.e. 35), bis-carbonium dications have been studied by theoretical methods. Examination of the potential energy surface of C3Hio2+ (diprotonated propane) finds three structures at energy minima.18 The global minimum corresponds to the structure (37) in which both terminal carbons are involved in electron-deficient 2e-3c bonds. The next most stable C3Hio2+ structure (38) lies 6.7 kcal/mol higher in energy and it possesses two 2e-3c bonds,... 

Clear, unequivocal experimental evidence has by now been obtained for nonclassical ions such as the norbomyl cation.38 10 The bonding concept required to define nonclassical ions is simply to consider them as penta(or higher)-coordinated carbonium ions involving at least one two-electron three-center (or multicenter) bond, of which CH5+ (themethoniumion-carbonium ion) is the parent, asCH3+ (the methenium ion, methyl cation, carbenium ion) is the parent for trivalent carbenium ions. An example of a hexacoordinate carbonium ion is the pyramidal dication of Hogeveen.41... 

The conversion is thought to involve formation of the carboxonium ion (77) by protonation of the carbonyl oxygen, and subsequent protonation then occurs at the C-H bond. The resulting carboxonium-carbonium dication (78) possesses the maximum possible charge-charge separation for this bicyclic framework. Subsequently, an intermediate carboxonium-carbenium dication (79) is produced, which isomerizes to the tertiary -carbenium ion, and deprotonation provides the product enone (80). Similar distonic superelectrophiles are proposed in other rearrangements of terpenes in superacid.28... 

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