View : 19 Download: 0

Origin of the α-effect in nucleophilic substitution reactions of y-substituted phenyl benzoates with butane-2,3-dione monoximate and z-substituted phenoxides: Ground-state destabilization vs. transition-state stabilization

Title
Origin of the α-effect in nucleophilic substitution reactions of y-substituted phenyl benzoates with butane-2,3-dione monoximate and z-substituted phenoxides: Ground-state destabilization vs. transition-state stabilization
Authors
Kim M.S.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. 12, pp. 2913 - 2917
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants (kNu-) have been measured for nucleophilic substitution reactions of Y-substituted phenyl benzoates (1a-i) with butane-2,3-dione monoximate (Ox-, an α-nucleophile) and Z-substituted phenoxides in 80 mol% H2O/20 mol% DMSO at 25.0 ± 0.1 °C. Hammett plots correlated with σ° and σ- constants for reactions of 1a-h with Ox- exhibit many scattered points. In contrast, the Yukawa-Tsuno plot results in a good linear correlation with ρY = 2.20 and r = 0.45, indicating that expulsion of the leaving group occurs in the rate-determining step (RDS). A stepwise mechanism with expulsion of the leaving-group being the RDS has been excluded, since Y-substituted phenoxides are less basic and better nucleofuges than Ox-. Thus, the reactions have been concluded to proceed through a concerted mechanism. Ox- is over 102 times more reactive than its reference nucleophile, 4-chlorophenoxide (4-ClPhO-). One might suggest that stabilization of the transition-state (TS) through intramolecular general acid/base catalysis is responsible for the α-effect since such general acid/base catalysis is not possible for the corresponding reactions with 4-ClPhO-. However, destabilization of the ground-state (GS) of Ox- has been concluded to be mainly responsible for the α-effect found in this study on the basis of the fact that the magnitude of the α-effect is independent of the nature of the substituent Y.
DOI
10.5012/bkcs.2009.30.12.2913
Appears in Collections:
자연과학대학 > 화학·나노과학전공 > Journal papers
Files in This Item:
There are no files associated with this item.
Export
RIS (EndNote)
XLS (Excel)
XML


qrcode

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

BROWSE