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A theoretical comparison of cationic and anionic homoaromaticity: Reinforcement of cationic homoaromaticity by σ‐nonclassical effects
Author(s) -
Wirth David,
Bauld Nathan L.
Publication year - 1980
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540010213
Subject(s) - cationic polymerization , mindo , isostructural , chemistry , ion , computational chemistry , generalization , planar , crystallography , organic chemistry , molecule , mathematics , crystal structure , computer science , mathematical analysis , computer graphics (images)
A MINDO/3 study of homoaromaticity in the 3‐cyclobutenyl cation and the Mobius 3‐cyclobutenyl anion has been used to evaluate cationic and anionic homoaromaticity quantitatively. π Homodelocalization energies of the two are found equal in isostructural planar comparisons. In planar optimized structures, the homodelocalization energy of the cation is slightly (about 4 kcal) greater than that of the anion, a consequence of the greater 1,3 distance in the latter. Full optimization produces a highly puckered and further stabilized cation, but engenders no change in the Mobius anion. The total stabilization of the cation relative to the anion is 13 kcal, in accord with the generalization that cationic homoaromaticity is more potent than the anionic variety. The fully optimized cation is revealed to actually have a much smaller π homodelocalization energy than the optimized anion, in contrast to the order of overall stabilities. σ‐Nonclassical effects, which are stabilizing in the cation but destabilizing in the Mobius anion, provide the rationale for the above.