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Kinetics and mechanism of reaction of p-methoxystyrene and tetracyanoethylene. I. Evidence for competitive 1,2- and 1,4-cycloadditions

✍ Scribed by Y. Uosaki; M. Nakahara; J. Osugi

Publisher
John Wiley and Sons
Year
1982
Tongue
English
Weight
470 KB
Volume
14
Category
Article
ISSN
0538-8066

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✦ Synopsis

Abstract

Time‐resolved absorption spectra for a reaction mixture of p‐methoxystyrene and tetracyanoethylene (TCNE) are found to have a band maximum at 325 nm which is assigned to the 1,4‐cycloadduct. The reaction in chloroform at 15, 20, and 25°C is followed by the charge‐transfer band at 600 nm. The 1,4‐cycloadduct, besides the so far known 1,2‐cycloadduct and EDA complex, is taken into account to derive the rate equation for the EDA complex that is a linear second‐order differential equation. The rate constants for the elementary steps involved in the reaction are obtained. The 1,4‐cycloaddition has an activation entropy of ‐63 J/K·mol for the cycloreversion and a reaction constant ρ of ‐4.7, both of which indicate the polar transition state. On the other hand, activation entropy of the 1,2‐cycloaddition is 73 J/K·mol more negative than that of the 1,4‐cycloaddition, supporting the zwitterionic mechanism for the 1,2‐cycloaddition.

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