Kinetics and Mechanism of 1,4-Cycloaddition between Tetracyanoethylene and Styrenes. II. Effect of Para Substituents

Article abstract of DOI:10.1246/bcsj.54.3681

The 1,4-cycloaddition of TCNE to p-methyl-, p-chloro-, and p-bromostyrenes by way of the EDA complex has been studied in chloroform at 25 deg C by the spectrophotometric method.The Hammett correlation obtained from the kinetic data provides -5.5 +/- 0.2 as the reaction constant ρ.The negative value is large in magnitude relative to other common 1,4-cycloadditions, suggesting some large partial charges in the rate-determining transition state.A linear correlation between the logarithmic forms of the reaction rate and the EDA-complex formation constant is in favor of the reaction scheme where the complex is on the pathway of the cycloaddition.