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Kinetics and mechanism of reaction of p ‐methoxystyrene and tetracyanoethylene. I. Evidence for competitive 1,2‐ and 1,4‐cycloadditions
Author(s) -
Uosaki Y.,
Nakahara M.,
Osugi J.
Publication year - 1982
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550140904
Subject(s) - tetracyanoethylene , chemistry , cycloaddition , reaction rate constant , photochemistry , kinetics , reaction mechanism , computational chemistry , catalysis , organic chemistry , quantum mechanics , physics
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.