Degree of inversion

Results of quantum-mechanical calculations (Dunitz and Orgel, 1957) have given values for the OSPEs of a number of transitional metal ions and the degree of inversion of mixed spinels... 

Organolithium reagents in which the carbanion is delocalized are more useful than alkyllithium reagents in alkylation reactions. Allyllithium and benzyllithium reagents can be alkylated and with secondary alkyl bromides and a high degree of inversion of configuration is observed.78... 

Arbitrary intermediate states also exist between normal and inverse spinels they can be characterized by the degree of inversion X ... 

In practice, however, the expected racemisation—and nothing but racemisation—is rarely observed, it is almost always accompanied by some degree of inversion. The relative proportions of the two are found to depend on (a) the structure of the halide, in particular the relative stability of the carbocation to which it can give rise and (ft) the solvent, in particular on its ability as a nucleophile. The more stable the carbocation, the greater is the proportion of racemisation the more nucleophilic the solvent, the greater is the proportion of inversion. These observations become understandable if the rate-limiting SN1 ionisation follows the sequence ... 

The reaction of 1-alkoxypolyfiuoroalkyl sulfonates with lithium tetraalkyl alumin ates yields stereospecifically alkylated products with a high degree of inversion. However, the reaction with trialkylaluminium reagents is considerably less stereospecific. 

Table 1.19 Lattice energy and CFSE for selected spinel compounds. Values of U, E, and from Ottonello (1986). CFSE values calculated with values proposed by McClure (1957). Data in kJ/mole x = degree of inversion.

There are two main points of interest. First, the extent of inversion varied over a wide range, and second, the high degree of inversion found for the aminodeoxy-scyiio- (46) and 3-amino-3-deoxy-chiro-inositol acetates was in marked contrast to the predominant retention of configuration observed in the deamination of simple, equatorial amines. 

Page 115) Not only does steric hindrance predict the retention/inversion ratio, but also the nature of the leaving group. In halopropionyl halides the degree of inversion for 34mCl-for-X substitution is... 

The occurrence of vacancies requires the adoption of two definitions of the degree of inversion, depending on the hypothesis made about the vacancies. Tetrahedral hypothesis . ft measures the concentration of indium in tetrahedral positions with respect to the maximum possible concentration. Octahedral hypothesis /3 measures the concentration of magnesium in octahedral positions with respect to the maximum possible concentration. 

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