Electrochemical study of beta-nitrostyrene derivatives: steric and electronic effects on their electroreduction

The electrochemical reduction of a series of beta-nitrostyrene and beta-met hyl-beta-nitrostyrene derivatives: by tast and differential pulse polarogra phy and cyclic voltammetry over a wide pH range was studied. The reduction potentials are sensitive to the electronic properties of the para-substitue nt and to the substitution at C beta. An increase in the electron-donor pro perties of the substituent at the para position makes the reduction potenti al more negative. On the other hand, the reduction potential shifts several tens of millivolts towards more negative potentials on going from beta-nit rostyrene to beta-methyl-beta-nitrostyrene derivatives, due to the decrease in conjugation with the increase in the C1-C alpha torsion angle. A linear correlation between the calculated electronic barrier and the half-wave po tential was observed. Furthermore, a linear correlation between the Hammett sigma(p) substituent constant and the half-wave potential also was observe d, demonstrating that the electrochemical behaviour of these derivatives de pends primarily on molecular structure and electron density distribution in a way similar to rates and equilibrium of homogeneous chemical reaction. T he beta-nitrostyrenes studied illustrate nicely the effects of steric and e lectronic: effects on electrochemical reactions. (C) 1999 Elsevier Science S.A. All rights reserved.