136272-23-6Relevant articles and documents
Silicon Effects. II. Structure and Stability of 1-Phenyl-2-(trimethylsilyl)ethyl Cation in Solution
Shimizu, Nobujiro,Watanabe, Shin-ichiro,Tsuno, Yuho
, p. 2249 - 2254 (2007/10/02)
Solvolysis rates have been measured in various solvents at 25 deg C for 1-(substituted phenyl)-2-(trimethylsilyl)ethyl trifluoroacetates (1a - 1g; R=H, 4-Me, 4-Cl, 4-Br, 3-Cl, 3,4-Cl2, and 3,5-Cl2, respectively) and structurally related compounds, 1-phenylethyl-, 3,3-dimethyl-1-phenylbutyl-, and 1-(4-methylphenyl)ethyl trifluoroacetates (3a, 4, and 5).In dioxane/water mixtures 1g solvolyzes with the same sensitivity to the change in solvent ionizing power as that for a kc substrate 5.The solvolyses of 1e and 5 exhibit almost identical α-deuterium kinetic isotope effects (kH/KD) of 1.18 - 1.19 in aq dioxane.Substituent effect on the solvolysis of 1 in 90 percent aq dioxane is expressed by an LArSR equation: log kX/kH = -3.05 (?0 + 1.05 Δ?(mean)+R) (R = 0.9997).These findings are consistent with kc mechanism for the solvolysis of 1.Relative rates for the solvolysis of 1a, 3a, and 4 in 30 percent aq dioxane are 2.99x105:2.84:1.0 indicating solvolytic generation of α-(trimethylsilylmethyl)benzyl cation to be about 7 kcal mol-1 energetically more favorable than that of the corresponding α-alkylbenzyl cations.
