Structural and energetic characterization of ylidenemalonodinitrile tautomers, precursors of fungicidal species

Ylidenemalonodinitrile (3,3-bis(4-chlorophenyl)-1-propene-1,1-dicarbonitrile), precursor of fungicidal compounds, synthesized in Knoevenagel reaction appears in solution in two forms, not separable by TLC chromatography. The ratio of both forms: that predicted from the Knoevenagel condensation scheme, and the second one, was preserved in the recrystallization cycle, as estimated fromNMR spectra. It was assumed that forms corresponding to two tautomers originated by shifting a carbon–carbon double bond CAryl2HC–CHyC(CN)2 vs. Aryl2CyCH–CH(CN)2). Crystal structure analysis identified in the solid state only one tautomer corresponding to the first form dominating in solution. In the refined model of the crystal structure both CyC bond and relevant hydrogen atoms were located univocally. Energy calculations carried out in vacuum and in solution confirmed energetic preference for tautomer present in the solid state. q 2003 Elsevier B.V. All rights reserved. PACS: 82.30.Qt; 61.10.-i