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A kinetic study on nucleophilic substitution reactions of phenyl y-substituted-phenyl carbonates with z-substituted-phenoxides: Effect of modification of nonleaving group from benzoyl to phenyloxycarbonyl on reactivity and reaction mechanism

Title
A kinetic study on nucleophilic substitution reactions of phenyl y-substituted-phenyl carbonates with z-substituted-phenoxides: Effect of modification of nonleaving group from benzoyl to phenyloxycarbonyl on reactivity and reaction mechanism
Authors
Min S.-W.Kim M.-Y.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2012
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 33, no. 10, pp. 3253 - 3257
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants for the reactions of phenyl Y-substituted-phenyl carbonates 5a-g with Zsubstituted- phenoxides (kZ-PhO-) have been measured spectrophotometrically in 80 mol % H 2O/20 mol % DMSO at 25.0 ± 0.1 oC. 4-Nitrophenyl phenyl carbonate (5e) is up to 235 times more reactive than 4- nitrophenyl benzoate (4e). The Brønsted-type plot for the reactions of 5e with Z-substituted-phenoxides is linear with β nuc = 0.54, which is typical for reactions reported previously to proceed through a concerted mechanism. Hammett plots correlated with σ° and σ - constants for the reactions of 5a-f with 4-chlorophenoxide exhibit highly scattered points. In contrast, the Yukawa-Tsuno plot results in an excellent linear correlation with ρY = 1.51 and r = 0.52, indicating that the leaving-group departure occurs at the rate-determining step (RDS). A stepwise mechanism, in which leaving-group departure occurs at RDS, has been excluded since the incoming 4-ClPhO - is more basic and a poorer nucleofuge than the leaving Y-substituted-phenoxides. Thus, the reaction has been concluded to proceed through a concerted mechanism. Our study has shown that the modification of the nonleaving group from benzoyl to phenyloxycarbonyl causes a change in the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway) as well as an increase in the reactivity. © 2005 KCSNET.
DOI
10.5012/bkcs.2012.33.10.3253
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자연과학대학 > 화학·나노과학전공 > Journal papers
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