Structural requirements favoring

In 1979, based on our work on methylchrysenes and on literature data on other methylated PAH, we suggested that the structural requirements favoring tumorigenicity of methylated PAH were a bay region... 

In order to investigate the structural requirements for the strong redox dependence, AEia values were also measured for anthraquinone, 12, and benzyl, 13, in the presence of 5 equivalents of diphenylurea in DMF. Under these conditions, phenan-threnequinone gives a shift of 61 mV, whereas anthraquinone gives a shift of only 8 mV and benzil 5 mV. Unlike phenanthrenequinone, the urea can only H-bond to one carbonyl oxygen at a time with anthraquinone. Two bifurcated H-bonds are possible, but these together would be much weaker than the two close to linear H-bonds possible with oquinones. A similar situation arises with benzil, since rotation about the central —C bond will be hindered in the radical anion and the favored conformation will have the oxygens trans due to electrostatic repulsion and steric effects. 

The change from calcite to vaterite nucleation on stearate films at low [Ca] suggests that the extent of Ca binding is important for polymorph selection. The nucleation of calcite is favored by the formation of a well-defined Ca-carboxylate layer that mimics the first layer of the (110) face of the unit cell. By contrast, the structural requirements for vaterite formation are less precise. This is consistent with vaterite being the dominant phase on amine monolayers where no Ca binding is present, and suggests that kinetic factors of charge accumulation... 

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