Abstract
Substituent Effects on the Solvolysis of 1-t-Butyl-2-(dimethylphenylsilyl)ethylTrifluoroacetates.Alam Md. Ashadul, Uddin Md. Khabir, Ryoji Fujiama, Mizue Fujio, and YuhoTsuno .The β-Si-substituent stabilizes extensively the carbocationic center and the so-called β-siliconeffect is the most powerful participating mechanisms in the carbocationic reactions. Manystudies have been attempted to elucidate the cation-stabilizing mechanism with the β-silicon effectin the carbocationic solvolysis in terms of either the open-cation form via s-p hyperconjugation orthe Si-bridged form via Si-participation.Hammett-type aryl-substituent effect has played an important role for elucidation of thetransition state structure in terms of charge distributions. Therefore, we have carried out the analysisof the aryl-substituent effects on Si atom in the various β-silylethyl systems. In this study, we havechosen the solvolysis of 1-t-butyl-2-(dimethylphenylsilyl)ethyl trifluroacetates having stericallycongested α-t-butyl group on the ethylene chain and the substituent effect on the solvolysis rates in60% aq. EtOH at 50°C was analyzed by the Yukawa-Tsuno Equation. The aryl-substituent effectwas found to give a linear correlation with ρ = -1.47 and r = 0.13 for the wide range of substituentsfrom p-MeO to 3,5-(CF3 )2 .
