Indenylidene dications antiaromaticity

Fluorenylidene and Indenylidene Dications Insights about Antiaromaticity... 

The results from studies on fluorenylidene dications such as 8 demonstrate clearly that species of this type are antiaromatic. However, extension of these studies to indenylidene dications such as 13 has important advantages. The... 

To perform a similar evaluation for the indenyl cation, 18, we must examine the bis-indenylidene dication, 19, and the appropriate data for both systems is given in Table IV. While 19 is more antiaromatic than 18 by all measures, the dependence of the measure of aromaticity and presumably antiaromaticity on ring size requires that the values for 19 be divided by 2. When examined in this manner, the indenyl cation 18 is more antiaromatic than 19, in contrast to the behavior of the fluorenyl system in 7 and 3. 

We have not yet prepared the unsubstituted indenylidene fluorene dication 17 but the NICSO) (18) values demonstrate that the fluorenyl cation is still more antiaromatic than the indenyl cation, see Table III. 

We have demonstrated that oxidation of fluorenylidenes and indenylidenes results in the formation of dications with appreciable antiaromaticity. The antiaromaticity of these species was examined for a series of dications from... 

The antiaromaticity of indenyl cations was examined in the dications of indenylidene fluorenes. Contrary to expectation, the fluorenyl cation was more antiaromatic than the indenyl cation in these systems. The sum of NICS(l)zz values was linearly related to global measures of antiaromaticity such as A, suggesting that they could be used to evaluate antiaromaticity in a local sense, for individual rings. 

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