Silicon Effects. V. β-Silicon Effect in the Solvolysis of 2-Phenylethyl Compounds

The rates of the solvolysis of 2-aryl-2-(trimethylsilyl)ethyl compounds, ArCH(SiMe3)CH2X (4: X = Cl and OCOCF3; Ar = C6H5 and p-MeOC6H4), have been measured in various solvents at 25°C. The solvolysis of the chloride, 4 (X = Cl; Ar = C6H5), exhibited an m value of 0.90 in aqueous dioxane consistent with rate-determining ionization; it gave (2-ethoxy-2-phenylethyl) trimethylsilane together with styrene in ethanol indicating a 1, 2-SiMe3 migration during the solvolysis. The p-MeO-substitution effect, kp–MeO/kH, was measured with the trifluoroacetates to be 2.1, in contrast to a factor of 269 observed in solvolysis of 1-aryl-2-(trimethylsilyl)ethyl compounds (1), indicating that distinct intermediates are involved in ionization of the two regioisomeric systems, 1 and 4.