Silicon Effects. II. Structure and Stability of 1-Phenyl-2-(trimethylsilyl)ethyl Cation in Solution.
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概要
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Solvolysis rates have been measured in various solvents at 25°C for 1-(substituted phenyl)-2-(trimethyl-silyl)ethyl trifluoroacetates (<B>1a</B>–<B>1g</B>; R=H, 4-Me, 4-Cl, 4-Br, 3-Cl, 3,4-Cl<SUB>2</SUB>, and 3,5-Cl<SUB>2</SUB>, respectively) and structurally related compounds, 1-phenylethyl-, 3,3-dimethyl-1-phenylbutyl-, and 1-(4-methylphenyl)ethyl trifluoroacetates (<B>3a</B>, <B>4</B>, and <B>5</B>). In dioxane/water mixtures <B>1g</B> solvolyzes with the same sensitivity to the change in solvent ionizing power as that for a <I>k</I><SUB>c</SUB> substrate <B>5</B>. The solvolyses of <B>1e</B> and <B>5</B> exhibit almost identical α-deuterium kinetic isotope effects (<I>k</I><SUB>H</SUB>⁄<I>k</I><SUB>D</SUB>) of 1.18–1.19 in aq dioxane. Substituent effect on the solvolysis of <B>1</B> in 90% aq dioxane is expressed by an LArSR equation: log<I>k</I><SUP>X</SUP>⁄<I>k</I><SUP>H</SUP>=−3.05 (σ<SUP>°</SUP>+1.05Δ\barσ<SUB>R</SUB><SUP>+</SUP>) (<I>R</I>=0.9997). These findings are consistent with <I>k</I><SUB>c</SUB> mechanism for the solvolysis of <B>1</B>. Relative rates for the solvolysis of <B>1a</B>, <B>3a</B>, and <B>4</B> in 30% aq dioxane are 2.99×10<SUP>5</SUP> : 2.84 : 1.0 indicating solvolytic generation of α-(trimethylsilylmethyl)benzyl cation to be about 7 kcal mol<SUP>−1</SUP> energetically more favorable than that of the corresponding α-alkylbenzyl cations.
- 公益社団法人 日本化学会の論文
著者
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Tsuno Yuho
Department Of Chemistry Faculty Of General Education Kumamoto University
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Shimizu Nobujiro
Department Of Chemistry Faculty Of Science Kyushu University
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Watanabe Shin-ichiro
Department of Applied Biological Chemistry, Faculty of Agriculture, Tohoku University:(Present)P.C. Center
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Tsuno Yuho
Department of Chemisty, Faculty of Science, Kyushu University
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