Thermolysis kinetics of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)succinates

摘要

An experimental approach was developed to determine the intrinsic thermolysis rate constants of the central carbon-carbon bond during the dl/meso isomerization of diethyl 2,3-dicyano-2,3-di(p-substituted phenyl)succinates (G=H, Me, OMe, Cl, and NO _2) at temperatures ranging from 80 to 120 °C. The obtained rate constants are significantly affected by the polarity of the para substituents, in sharp contrast to their negligible effects on the dl/meso isomerization equilibrium constants. Moreover, the substituent effects on the activation enthalpies can be linearly correlated with the Hammett substituent resonance constants and the homolytic dissociation enthalpies (bond dissociation energies) of the benzylic C-H bonds of ethyl 2-cyano-2-(p- substituted phenyl)acetates.