Electrochemical study of beta-nitrostyrene derivatives: steric and electronic effects on their electroreduction
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The electrochemical reduction of a series of beta-nitrostyrene and beta-methyl-beta-nitrostyrene derivatives: by tast and differential pulse polarography and cyclic voltammetry over a wide pH range was studied. The reduction potentials are sensitive to the electronic properties of the para-substituent and to the substitution at C beta. An increase in the electron-donor properties of the substituent at the para position makes the reduction potential more negative. On the other hand, the reduction potential shifts several tens of millivolts towards more negative potentials on going from beta-nitrostyrene 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 potential was observed. Furthermore, a linear correlation between the Hammett sigma(p) substituent constant and the half-wave potential also was observed, demonstrating that the electrochemical behaviour of these derivatives depends primarily on molecular structure and electron density distribution in a way similar to rates and equilibrium of homogeneous chemical reaction. The beta-nitrostyrenes studied illustrate nicely the effects of steric and electronic: effects on electrochemical reactions.