Gitonic Vicinal Superelectrophiles

Superelectmphiles and Their Chemistry, by George A. Olah and Douglas A. Klumpp Copyright 2008 John Wiley Sons, Inc. 

While both 4-phenylbutyronitrile (6) and 1,3-diphenyl-l-propanone (9) cyclizations show a dependence on acid strength, the kinetic data suggest differing degrees of protonation at their transition states, or differing protosolvation of the activated complexes. 

Vicinal 1,2-carbodicationic systems are some of the most important and thoroughly studied superelectrophiles. They include inter alia 1,2-ethylene dications, related carbon-nitrogen superelectrophiles (diprotonated imines and nitriles), protosolvated carboxonium ions, and superelectrophilic tri-halomethyl cations. It is understood that many of these systems involve extensive charge delocalization, and in a sense may not be considered formal 1,2-dicationic systems. For example, diprotonated 2,3-butanedione (34) may be represented formally as a 1,2-ethylene dication (35a, a gitonic superelectrophile), but even in monocationic carboxonium ions, there is a significant amount of double-bond character retained in the carbon-oxygen bond (eq 5).22 

Charge-charge repulsive effects increase the importance of the resonance form (35b) having dione-type structure (a 1,4-dication and representing a distonic superelectrophile). Despite the importance of the charge separated structure 35b, the system is included here with other 1,2-ethylene dications and gitonic superelectrophiles. 

1 Carbon-Carbon Vicinal-Dications Ethylene dications are a major group of carbon-centered superelectrophilic systems. The parent ethylene dication (CH2CH22+, 1) has been studied experimentally in the gas-phase, as well as in several theoretical studies.1 Two electron 

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