Mills-Nixon theory

S. Ziller, J. X-ray diffraction evidence for a cyclohexatriene motif in the molecnlar structure of tris(bicyclo[2.1.1 ]hexeno)benzene bond alternation after the refutation of the Mills-Nixon theory, Angew. Chem. Int. Ed. Engl 1995, 34, 1454-1456. 

FIGURE 6.12 Traditional application of the Mills-Nixon effect theory to a-tocopherol-type henzopyranols and benzofuranols, having an anullation angle sum of (a + (3). 

The Mills-Nixon hypothesis had, as its foundation, certain differences in the chemical behaviour of indan (3) and tetralin (4) from which a localization of the aromatic 7r-bonds was predicted to occur in the direction depicted by la rather lb. The original experimental evidence upon which the effect was based was shown to be erroneous, but calculations at various levels of theory indicated that aromatic bond localization should exist and become more pronounced as the size of the annelated ring decreases In essence one can recognize that the structure of benzene has a symmetry such that both Kekule structures must contribute equally. With Q tetralin (4) (and the lower homologues) no such symmetry requirement exists and ring annelation could induce bond length alternation within the arene nucleus. As the strain imposed by the fused ring increases, the Mills-Nixon effect should increase. The hypothesis has been the subject of considerable discussion and the controversy is far from settled. 

A wave-mechanical treatment of the Mills-Nixon effect. Trans. Faraday Soc. 31 (1935) 939-945. (L. E. Sutton and Linus Pauling). (SP 12 Remarks on the theory of aromatic free radicals. J. Chem. Phys. 3 (1935) 315. (Linus Pauling and G. W. Wheland). 

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