The Realities of Extended Homoaromaticity

Abstract

Homoaromaticity has been the subject of many investigations and continues to remain an extraordinarily rich area of chemistry. Quantitative experimental evaluation of the level of long range delocalization and assessment of interactions in molecules having two or more insulating atoms, together with various theoretical estimates of energies and geometries, are areas currently being examined. The primary intention of this review is to provide a critical up-to-date survey of relevant spectral and structural data, as well as an analysis of the many reactions believed to involve generation of homoaromatic ions. Extensively discussed are mono-, bis-, and trishomoaromatic systems arranged on the basis of their cationic, anionic, or uncharged nature. Presentation of these individualized segments is preceded by a brief analysis of homoaromatic overlap.

Application of the Cplex-isoelectronic theory to electrocyclisations, sigmatropic rearrangements, cheletropic reactions and antiaromaticityConsistent with Santilli's hadronic chemistry

“…Hence an aromatic molecule must generate a diamagnetic field in the presence of an applied field but its presence does not imply aromaticity. The anisotropic structure of the induced diamagnetic ring currents in these systems [42] implies valence tautomerism as oppose to a single state for these cations. Moving isoelectrons create an anisotropic effect [75].…”

“…16), [42] cannot benefit from RCEDGD stability as syn FSED is not feasible [1] and thus is predicted not to be 'aromatic'. The diamagnetism can be explained by nonneutralised FSED delocalisation with the isoelectron pair also moving through the space between C-1 and C-3.…”

“…The existence and the threedimensional structure of the monohomocyclopropenium cation [42] and bicyclobutane opens the possibility that carbon ( [1,3] C) can tolerate the necessary strain (bridging methylene group over a 3 atom system). Furthermore, bending and stretching modes of the single bond can be involved, as relatively high temperatures are required, up to 573 K, and thus distorted geometries are feasible.…”

Cyclic homoconjugation in neutral organic molecules

“…Cyclic homoconjugation involving 4N+2 electrons, for example, has been found to endow a variety of carbocations with aromatic properties (ref. [1][2][3]. Among these homoaromatic ions, the homotropylium ion occupies a position comparable in prominence to that held by benzene within the family of aromatic molecules (ref.…”

Multicenter Bond Indices As a New Means for the Quantitative Characterization of Homoaromaticity

“…Because of its importance, the phenomenon of homoaromaticity has been the subject of a wealth of experimental and theoretical studies aiming both at the evaluation of various manifestations of this phenomenon [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and, also, to the design of new tools and procedures allowing estimating the extent of the effects responsible for its existence. An example can be, e.g., the early studies [10][11][12][13] in which qualitative molecular orbital (MO) diagrams and perturbational MO (PMO) theory were used to estimate the energetic impact of homoaromatic stabilization.…”