Occurrences oxidation, stereochemistry

Finally, we reemphasize that the occurrence of a given oxidation state as well as its stereochemistry depend very much on the experimental conditions and that species that cannot have independent existence under ordinary conditions of temperature and pressure in air may be the dominant species under other conditions. In this connection we note that transition metal ions may be obtained in a configuration that is difficult to produce by other means through incorporation by isomor-phous substitution in a crystalline host lattice, for example, tetrahedral Co3+ in other oxides, tetrahedral V3+ in the NaAlCL, lattice, as well as by using rigid ligands such as phthalocyanins. 

Slow tram addition of nitrosyl chloride to steroid-5-enes was observed123- 1 26 however, the initially formed chloro nitroso adducts were oxidized by nitrosyl chloride to the 5a-chloro-6/ -nitro derivatives 1 dimerization does not occur for steric reasons. The diaxial configuration of adducts was deduced by the ready elimination of the chloro and nitro groups by zinc dust123, and from the H-NMR spectrum125,126. The stereochemistry can be explained by the occurrence of both ionic and free-radical mechanisms124. 

As to the stereochemistry of the newly identified epoxy-lina-lool oxides(26-33) only differentiation between (Z)- and (E)-isomers can be provided at present. Using HRGC-FTIR technique (Figures 10 and 11) the occurrence of an intramolecular H-bonding in two dia-stereoisomers indicated (Z)-configuration. These bands were detected at 3490 cm-1 and 3525 cm-1 in the pyranoid and furanoid (Z)-config-urated derivatives, respectively. 

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