Mills-Nixon effect, and

The idea that distortion of a benzene ring to produce alternating longer and shorter bonds could produce localization of the 7t-electron density is known as the Mills-Nixon effect and has been the subject of much debate in organic chemistry. An experimental result that is consistent with a particular model is supportive evidence for that model, but it can never be considered conclusive. For example. Mo and Schleyer found that bond alternation would not necessarily decrease the aromaticity of a 1,3,5-cyclo-hexatriene and that the heat of hydrogenation of 1 could be the result of other factors, such as the avoidance of antiaromaticity in the four-membered... 

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