Cis-trans-Isomerie bei 1-Amino-3-imino-propenen (Basen der Trimethincyaninreihe) am Beispiel des Malonaldehyddianils

Abstract

It has been proved possible to establish relationships between charge, configuration and spectroscopic properties of the chromophoric system N-C-C-C-N containing 6 π-electrons. This system occurs in an uncharged form in the amino-imino-propenes. In the case of malonaldehyde-dianil, spectroscopic (u.v. and n.m.r.) data indicate that 1-amino-3-imino-propenes exist in a cis-trans equilibrium which is solvent and temperature dependent. The position of the equilibrium may be correlated with the tendency of the solvent to form hydrogenbonds. Cis-trans conversion of these compounds may also be effected by irradiation. The half-life for the interconversion of malonaldehyde-dianil in n-hexane at room temperature has been measured by flash spectroscopy and found to be τ½=140± 10 msec. In contrast to the photochemical transeis conversion found in cyanine cations and polyenes, the present phenomenon is a cis-trans rearrangement.