G. Olah, John S. Staral
Sep 1, 1976
Citations
0
Influential Citations
35
Citations
Journal
Journal of the American Chemical Society
Abstract
The tetraphenyl(2), 1,2-difluoro-3,4-diphenyl (6), 1,2-diphenyl(7), and tetramethylcyclobutadiene (5) dications have been prepared under stable ion conditions and studied by 'H, '9F , and 13C NMR spectroscopy. The 13C NMR spectra of the phenylated cyclobutadiene dications indicate that the aromatic 2r-electron cyclobutenediylium ring interacts mesomeri. cally with the phenyl rings and accepts a significant amount of a-electron density from them . The degree of conjugative interaction between phenyl substituents and the aromatic cation is shown to be greater in the cyclobutadiene dication system than in the cyclopropenium system . Evidence has also been obtained for the existence of the 1,2-dimethylcyclobutadiene dication, which is quenched in superacidic solution to the related 4.fluorocyclobutenyl cation by the fluoroantimonate counterion. These results are discussed in terms of the relative ability of phenyl and alkyl substituents to contribute to stabilization of cations (dications) in the cyclobutadiene and cyclopropene systems . Further, a rationale is provided for the reversal of the trends observed in these two Hfcckeloid systems. The question as to whether the NMR spectroscopic observations of cyclobutadiene dications correspond to several species in dynamic equilibrium or to static, nonequilibrating dications has also been systematically investigated and unequivocal evidence for the latter is presented.