Gitonic

The protonation of the methyleneiminium cation gives rise to the superelectrophilic methyleniminium dication, 19, which is a gitonic 1,2-dicationic species (carbenium ammonium species). Such a carbodication has been observed by charge stripping mass spectrometry by Schwarz and coworkers.Olah and coworkers have shown by theoretical calculations that the carbenium ammonium species, 19a, is 27.6 kcal/mol more stable than the three-center two-electron (3c-2e) bonded structure, 19b. ... 

The dimethylation of methyl acetate (methylation of the 1,1-dimethoxyethyl cation) was calculated to form two isomeric gitonic dications (303), which are thermodynamically more stable than the neutral ester.578 They are expected to be involved in the observed methyl exchange of 1,1-dimethoxyethyl cation. Rotamer 303b is more stable than the isomeric dication 303a, by 10.0 kcal mol-1 (MP2/6-31G //MP2/6-31G +ZPE level). 

On the potential energy surface of diprotonated propane (C3H102+), three structures were located as minima (MP2/6-31G level).788 The 1 -//,2-//-diprotonated and 1-/7,3-//-diprotonated forms (458 and 459) are of Cj and C2v symmetry, respectively, whereas the l-//,C-diprotonated structure (460) has C symmetry. Structure 459, a distonic dication with the two charge-bearing centers separated by one carbon, is significantly more stable (by 22.6 kcal mol-1) than structure 458 (a gitonic dication with adjacent charges) and also more stable than structure 460 (by 6.9 kcal mol ). 

For diprotonated isobutane (C4H122+) the structures found as stable minima are analogous to those computed for diprotonated propane (C3H102+). Again, structure 478 (a distonic dication) is 17.7 kcal mol 1 more stable than structure 479 (a gitonic dication), whereas structure 480 is only slightly less stable than 478 (2.6 kcal mol-1).788... 

Superelectrophilic intermediates have been categorized into two distinct groups the distonic (distant) and the gitonic (close) superelectrophiles (Table l).22 Distonic superelectrophiles are defined as electrophiles in... 

There have been many studies related to tetraaryl-1,2-ethylene dications, formally gitonic superelectrophiles, which show extensive charge delocalization into the aryl rings (Scheme 1). Low temperature 13C NMR studies have shown that the para carbons are deshielded, from < 13C... 

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... 

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