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

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Abstract
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 °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.