Formation of Electron-Donor-Acceptor Complex and 1,4-Cycloadduct of Tetracyanoethylene with Styrene and Its α- or β-Substituted Derivatives

Article abstract of DOI:10.1246/bcsj.54.2569

EDA-complex formation and 1,4-cycloaddition of tetracyanoethylene (TCNE) with styrene, α-methylstyrene, 1,1-diphenylethylene, cis-stilbene, and trans-stilbene were studied spectrophotometrically in chloroform at 25 deg C.Formation constants of the EDA complexes were found to be in the order, trans-stilbene above styrene above α-methylstyrene above cis-stilbene above 1,1-diphenylethylene.The difference in the formation constants was discussed in terms of both electronic and steric effects of the donors studied. α-Methylstyrene and 1,1-diphenylethylene underwent thermal cycloaddition to TCNE faster than styrene.It is suggested that some charge separation took place in the transition state.The fact that trans- and cis-stilbenes do not react with TCNE was explained in terms of the difference in stability of the 1,4-cycloadducts estimated from the 1,4-bislocalization energy obtained by Dewar's perturbation molecular orbital method.