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Kinetics and mechanism of nucleophilic displacement reactions of Y-substituted phenyl benzoates with Z-substituted phenoxides

Title
Kinetics and mechanism of nucleophilic displacement reactions of Y-substituted phenyl benzoates with Z-substituted phenoxides
Authors
Min S.-W.Seo J.-A.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2009
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 30, no. 10, pp. 2403 - 2407
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants have been measured for two series of nucleophilic displacement reactions, i.e., reactions of 4-nitrophenyl benzoate with Z-substituted phenoxides and those of Y-substituted phenyl benzoates (1a-h) with 4-chlorophenoxide (4-ClPhO-) in 80 mol% H2O/20 mol% DMSO at 25.0 ± 0.1 °C. The Brønsted-type plot for reactions of 4-nitrophenyl benzoate with Z-substituted phenoxides exhibits an excellent linear correlation with βnuc = 0.72. Reactions of 1a-h with 4-chlorophenoxide result in also a linear Brønsted-type plot with βlg = -0.62, a typical βlg value for a concerted mechanism. The Hammett plots correlated with σ° and σ- constants show many scattered points for reactions of 1a-h with 4-chlorophenoxide. In contrast, the corresponding Yukawa-Tsuno plot exhibits an excellent linear correlation with ρY = 2.26 and r = 0.53, indicating that expulsion of the leaving group occurs at the rate-determining step (RDS) either in a concerted mechanism or in a stepwise pathway. However, a stepwise mechanism with leaving group departure being the RDS is excluded since the leaving Y-substituted phenoxide is less basic and a better nucleofuge than the incoming 4-ClPhO-. Thus, the reactions have been concluded to proceed through a concerted mechanism, in which bond formation between the nucleophile and electrophilic center is more advanced than expulsion of the leaving group in the transition state on the basis of the magnitude of βnuc and βlg values.
DOI
10.5012/bkcs.2009.30.10.2403
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자연과학대학 > 화학·나노과학전공 > Journal papers
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