Potential Homoantiaromatics

In the potentially homoantiaromatic molecules of Figure 11, electron delocalization occurs along the periphery of a bicyclic system, involving in this way Aq + 2 rather than 4 q electrons. Since, however, the corresponding orbital system is of Mobius rather than Hiickel type (Figure 9), delocalization of 4q + 2 electrons leads to overall destabilization rather than stabilization. 

A further key point to make is the desirability of examining related 4q as well as 4q + 2 systems. We believe that the results we have outlined in Sections III and V well demonstrate the additional information that comes in placing a potentially homoantiaromatic system in juxtaposition with its homoaromatic counterparts. Further work with the 4q systems is required in many series of systems. 

On the basis of initial H NMR studies and theoretical calculations. the bicyclo[3.1.0]hexenyl cation 41 was described as a potentially homoantiaromatic species that possessed the cyclic conjugated 47r-electron system represented by 41a. However. later theoretical studies of 41 and experimental studies of long-lived ions including 41, the cyclohexadienyl cation 41c. s and methylated derivatives such as 41h J were interpreted as indicating the ion was nonaromatic. The allylic ion 41 was reported to be stabilized by electron donation from the two external C—C bonds of the cyclopropyl group and not the Ci—C3 bond. A related example... 

We conclude that each case of potential bond or, more specifically, cyclopropyl homoantiaromaticity has to be considered separately. Detailed investigations have to clarify whether homoantiaromaticity is of any chemical relevance or whether the molecule has reorganized into a non-homoaromatic electronic structure. 

Contrary to bond homoantiaromaticity, very little is known about no-bond homoantiaromaticity123. In a potentially no-bond homoantiaromatic molecule, there is often the... 

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