Distortion of geometry

The discrepancy between physicochemical and reactivity criteria for aromaticity was known long ago. Yet the data procured by the studies of compounds like 186 or 189 shed a new light on this problem. The observed deviation from planarity did not cause any substantial changes in the spectral parameters of these compounds. Thus they still should be considered aromatic from the point of view of physical chemists. At the same time, this distortion of geometry so dramatically affected their reactivity pattern that, in accordance with this criterion, cyclophanes 186 or 189 should best be referred to as non-aromatic compounds, derivatives of 1,3,5-cyclohexatriene. ... 

The electrostatic potential of a chemical species, as normally calculated, reflects the net electrical effect of its nuclei and electrons in some fixed state. Thus V(r) does not typically take account of changes that may occur in a system as it begins to interact with an approaching molecule or ion, such as polarization or distortion of geometry, nor does it in any way reflect the nature of the approaching species. Because of these inherent limitations, the electrostatic potential is most useful as a guide to the early stages of a reaction, where these effects are relatively minor. It should be noted that procedures based on second-... 

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