The Yukawa–Tsuno Relationship for the β-Silicon Effect in the Solvolysis Rates of 2-(Aryldimethylsilyl)ethyl Chlorides

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Abstract
Solvolysis rates of 2-(aryldimethylsilyl)ethyl chlorides were determined conductimetrically in 60% (v/v) aqueous ethanol. The effects of aryl substituents at the silyl atom on the solvolysis rates at 50 °C were correlated with essentially nonresonant parameters of r = 0.10 in terms of Yukawa–Tsuno (Y–T) Eq. 1, giving a ρ value of −1.75. Such a high ρ value may be regarded as the effect of aryl ring on the bridged Si in the rate-determining step. The Si-bridging is consistent with the fact that the solvolysis of the unsubstituted substrate with d2-labeled ethylene moiety gave substitution products with label scrambling. The arylsilyl substituent effects were likewise analyzed for several relevant sets of β-silyl systems in order to ascertain significant variations of ρ values from system to system; Y–T Eq. 1 correlated quite excellently with essentially nonresonant sigmas of negligible resonance demand (r 0.10), to exhibit significant variations of ρ from −1.75 to −0.95.