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The β ‐silicon effect. 4: substituent effects on the solvolysis of 1‐alkyl‐2‐(aryldimethylsilyl)ethyl trifluoroacetates
Author(s) -
Fujiyama Ryoji,
Alam Md. Ashadul,
Shiiyama Aiko,
Munechika Toshihiro,
Fujio Mizue,
Tsuno Yuho
Publication year - 2010
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1667
Subject(s) - solvolysis , chemistry , substituent , silylation , alkyl , medicinal chemistry , aryl , aqueous solution , silicon , computational chemistry , organic chemistry , hydrolysis , catalysis
Solvolysis rates of 2‐(aryldimethylsilyl)‐1‐methylethyl and 2‐(aryldimethylsilyl)‐1‐ tert ‐butylethyl trifluoroacetates were determined conductimetrically in 60% (v/v) aqueous ethanol. The effects of aryl substituents at the silicon atom on the solvolysis rates at 50 °C were correlated with $\bar {\sigma }$ parameters of r + = 0.15 with the Yukawa–Tsuno equation, giving ρ values of −1.5 for both secondary α ‐Me and α ‐ tert ‐Bu systems. The ρ values for those secondary systems are less negative than −1.75 for the 2‐(aryldimethylsilyl)ethyl system that proceeds by the Eaborn (non‐vertical) mechanism, while they are distinctly more negative than −0.99 for 2‐(aryldimethylsilyl)‐1‐phenylethyl system that should proceed by the Lambert (vertical) mechanism. There was a fairly linear relationship between the reaction constants ( ρ ) for the β ‐silyl substituent effects and the solvolysis reactivities for a series of β ‐silyl substrates. The solvolyses of the α ‐Me and tert ‐Bu substrates proceed through the transition state (TS) with an appreciable degree of the β ‐silyl participation, close to the Eaborn (non‐vertical) TS rather than to the Lambert (vertical) TS. Copyright © 2010 John Wiley & Sons, Ltd.