2-(1-Isonicotinoylhydrazinoalkylidene)-5,5-dimethyl-1,3-cyclohexanediones and their polychromism. A new type of compound with intramolecular charge transfer through the hydrazonocarbonyl bridge

The product of condensation of 2-formyldimedone with the hydrazide of isonicotinic acid, namely 2-isonicotinoylhydrazinomethylene-5,5-dimethyl-1,3-cyclohexanedione, has been obtained in three forms — red, colorless, and yellow — which with methyl iodide give one and the same iodide 2-N-(1-methyl-4-pyridiniumcarbonyl)hydrazinomethylene]-5, 5-dimethyl-1, 3-cyclohexanedione. On the basis of UV spectra and x-ray structure analysis of this betaine and also the dark-red iodide of N-(4-diethylaminobenzal)-N-(1-methyl-4-pyridiniumcarbonyl)hydrazine, it has been shown that intramolecular charge transfer in these linear molecules proceeds along the system of bonds D:-RC=N-NH-CO-A through the hydrazonocarbonyl bridge, which does not interrupt the conjugation chain. The existence of colored forms of the 2-isonicotinoylhydrazinomethylene-5,5-dimethyl-1,3-cyclohexanedione can be explained by an admixture of the betaine form.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 489–498, April, 1993.