Steric effects cyclohexane derivatives

Conformational analysis is defined in a recent book by Eliel et al. (30) as an analysis of the physical and chemical properties of a compound in terms of the conformation (or conformations) of the pertinent ground states, and (in the case of spectra) excited states. For additional background see Stereochemistry of Carbon Compounds by Eliel (31), Steric Effects in Organic Chemistry by Newman (32), and The Stereochemistry of Cyclohexane Derivatives by Orloff (33). 

The conformational problems of cyclohexene derivatives are somewhat different than those observed with cyclohexanone or cyclohexane derivatives. The presence of the alkene moiety effectively flattens four carbons of the ring, which changes the different steric effects for substituents with an incoming reagent, relative to cyclohexanone derivatives. The most abundant conformations of cyclohexenone derivatives are 310 and 311. The first problem that arises in conjugated derivatives is the competition of 1,2- with 1,4-addition for... 

The relationship, A(oxane) = 1.53 A(cyclohexane) + 0.02, should also be valid for polar substituents if it expresses only an effect of bulkiness, due to the greater steric constraints at position 2 of oxane. It may be used to calculate their correct A value at this position and therefore derive a more significant value for the anomeric effect. Thus the minimum value of (9-methyl is recalculated as 2.1 kcal mol, a figure 60% higher than that in Table 2.3 (Franck 1983). 

In deriving equation 32 or equation 33, it is assumed that 0max is the solid volume fraction at which the suspended particles cease moving. Thus, the forces, such as shearing, that can disturb the suspension structure and hence improve the mobility of particles will have an effect on the value of max. This is confirmed by the fact that a value of kH = 6.0 is observed at low shear limit, that is, y 0 and at high shear limit, y - oo, kH = 7.1 is found. Typical values of max have been found with the use of Quemada s equation as 0max = 0.63 0.02 in the low shear limit and high shear limit for submicrometersized sterically stabilized silica spheres in cyclohexane (72, 85, 88). 

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