Oximes configurational stability

Owing to the relative rigidity of the carbon-nitrogen double bond, oximes can exist in two discrete geometrically isomeric forms the E or anti isomer anti-E-217) and the (Z) or syn isomer (syn-Z-217) (equation 70). In solid state, both oximes show high configurational stability and discrete existence. In solution, equilibrium between both isomers is rapidly established, favouring the thermodynamically most stable isomer " ... 

When electron-withdrawing groups are present on both the carbon and nitrogen atoms of the oxime, triazoline adducts ranging in yield from 23 to 89% are obtained by reaction with diazomethane or diazoethane (Scheme 102) the aziridines formed from these triazolines are found to show unusual configurational stability.363,364... 

Hantzsch was unable to provide any direct experimental proof for his hypothesis. His grounds for assigning configurations were the analogies to oximes, such as the differences in stability already mentioned. 

Another type of oximes, amino-oxime ligands, has been developed by the condensation of biacetyl monooxime with 2-(aminomethyl)pyridine and 2-(2-aminoethyl)pyridine. This tridendate ligand led to different stereoisomers. The stability of the various possible isomers of cobalt complexes 147 and 148 has been calculated. The minimum strain energy is observed for a w< r-configuration for imino complexes [Co(L )2] and amino complex [Co(L - )(HL )] + (Figure 43). 

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