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Ion radicals of substituted 2-furylethenetricarbonitriles (an ESR, quantum-chemical, and electrochemical study)

A. Staško, D. Berkeš, S. Biskupič, P. Pelikán, and J. Polakovič

Department of Physical Chemistry, Faculty of Chemical Technology, Slovak Technical University, CS-81237 Bratislava

Abstract: Substituted 2-(5-X-2-furyl)-l,l,2-ethenetricarbonitriles acceptors with X = CH₃, H, CI, Br, I, and CN cathodically reduced form stable anion radicals with electron spin density distributed over the whole molecule. However, if X = N0₂ the spin density is centred on nitro group (aN = 1.028 mT) and no spin density is observable on the ethenetricarbonitrile part of radical. The ESR spectra and INDO calculations imply the hindered rotation around the furyl—ethene bond. The reaction products of nitro derivative with arene or heteroarene donors are 2-(5-aryl- or heteroaryl-2-furyl)-1,1,2-ethenetricarbonitriles. Electrochemically they form cation resp. anion radicals with electron spin density centred on aryl resp. furylethenetricarbonitrile part of the molecule. Generally, the reactions are electrochemically reversible with a consecutive chemical reaction. By cyclic voltammetry measured redox potentials correlate well with the Hammett constants of substituents and with INDO calculations.

Full paper in Portable Document Format: 432a177.pdf

Chemical Papers 43 (2) 177–190 (1989)