Mills—Nixon effect

A WAVE-MECHANICAL TREATMENT OF THE MILLS-NIXON EFFECT... 

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). 

Behan, J. M. Dean, F. M. Johnstone, R. A. W. Photoelectron spectra of cyclic aromatic ethers the question of the Mills-Nixon effect. Tetrahedron 1976, 32, 167-171. 

Taylor has collected the above and similar data and compared the ratio of reactivities of the ortho and para positions of compounds of type 19 (expressed as log/odog/p) with the ratio of reactivities of the equivalent positions, a and c, in compounds of type 20 and found that the latter ratio was lower, i.e., a relative increase in the reactivity of the para position (c) has occurred upon ring formation. This fall in the ratio log fa log fc increases along the series X = S < 0 (< NH < CHg) in 20. As this trend parallels the increase in strain in the fused bridging ring it was argued that ring strain was the primary cause of the reduction in ratio. Position a is a-aromatic and position c is j8-aromatic therefore the above concept represents an extension by Taylor of an earlier explanation of the Mills-Nixon effect in indane. Further substitution... 

The manifestation of a Mills-Nixon effect in benzocyclopropene (1) was examined by a variety of methods. Thus examination of the PE spectra of cyclo-proparenes and appropriate model compounds provided no information on the question.Similarly, NMR investigations using vicinal coupling constants or orthobenzylic coupling constants, involving methyl-substituted cydoproparenes revealed no evidence for sterically induced bond fixation. Theoretical calculations led to contradictory results. Early extended Hiickel calculations supported the concept in indanes but in the opposite sense than that suggested by Mills and Nixon. Semiempirical calculations for benzocyclopropene favored structure 258 over A substantial Mills-Nixon effect in the same direction resulted from... 

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