Osazones tautomeric structures

Fischer represented the hydrazones and osazones as open chain structures one sees at once, however, other structural possibilities since mutarotation occurs in solution in many cases. Unless this is due to decomposition, some form of tautomeric equilibrium must be postulated, and Haworth pointed out that cyclic structures must be considered Behrend and Lohr recognized the possibility of the existence of syn and anti forms, and it has also been suggested that there may be an equilibrium between hydrazone and azo structures in the osazones. 

It will be seen that the cleavage of the hypothetical hydrazo derivatives to the hypothetical imino compounds obviates the necessity of assuming direct oxidation by phenylhydrazine. Fieser and Fieser inquire why osazone formation ceases with the introduction of two phenylhydrazine residues, and seek to explain this fact by the postulation of chelate tautomeric ring structures XLIII or to the existence of a resonance... 

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