Nitroenamines tautomerism

IR, UV and NMR spectra obtained so far are compatible with the structure of the secondary enamines. The tautomeric enamine structure of some enaminones in the solid state has also been established unambiguously by single-crystal X-ray diffraction analyses21. In agreement with the experimental evidence, theoretical calculations22,23 performed on enaminones 6-8 and nitroenamine 9 indicate that the enamine forms are... 

Nitroenamines with a primary or secondary amino group can exist also in two tautomeric forms the imino-nitro form (511) and the imino-nitronic acid form (512). Although the enamine form represents the thermodynamically more stable tautomer, the imino-nitro form has been observed when severe steric hindrance prevents planarity of the conjugated system Compounds 513, derived from 2-nitrocycloalkanones, have been reportedto exist exclusively as the imino-nitronic acid tautomer, although the spectroscopic evidence presented is also consistent with the enamine form,... 

Extensive studies have shown that the enamine-imine tautomeric equilibrium of equation 1 shifts almost completely to the enamine side when an unsaturated electron-withdrawing group including nitrile nitro °, carbonyl, thiocarbonyP etc. ° is attached to the -carbon. Reviews related to these enamines which include enaminoni-triles 2, nitroenamines 3, enaminones 4 and the enaminothioketones 5, have appeared in the literature, ... 

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