Silicon Effects. II. Structure and Stability of 1-Phenyl-2-(trimethylsilyl)ethyl Cation in Solution

• Nobujiro Shimizu

  Department of Chemisty, Faculty of Science, Kyushu University

• Shin-ichiro Watanabe

  Department of Chemisty, Faculty of Science, Kyushu University

• Yuho Tsuno

  Department of Chemisty, Faculty of Science, Kyushu University

抄録

Solvolysis rates have been measured in various solvents at 25°C for 1-(substituted phenyl)-2-(trimethyl-silyl)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% aq dioxane is expressed by an LArSR equation: logkX⁄kH=−3.05 (σ°+1.05Δ\barσR+) (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% aq dioxane are 2.99×105 : 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.

収録刊行物

• Bulletin of the Chemical Society of Japan

  Bulletin of the Chemical Society of Japan 64 (7), 2249-2254, 1991-07-01

  Oxford University Press (OUP)

キーワード

• General Chemistry

詳細情報

• CRID: 1360002219103549056
• NII論文ID: 130001978771
• DOI: 10.1246/bcsj.64.2249
• ISSN: 13480634
• ISSN: 00092673
• Web Site: https://academic.oup.com/bcsj/article-pdf/64/7/2249/56188743/bcsj.64.2249.pdf
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