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Kinetic and theoretical studies on pyridinolysis of 2,4-dinitrophenyl X-substituted benzoates: Effect of substituent X on reactivity and mechanism

Title
Kinetic and theoretical studies on pyridinolysis of 2,4-dinitrophenyl X-substituted benzoates: Effect of substituent X on reactivity and mechanism
Authors
Um I.-H.Kim E.-H.Im L.-R.Mishima M.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2010
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 31, no. 9, pp. 2593 - 2597
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants (k N) have been measured spectrophotometrically for reactions of 2,4-dinitrophenyl X-substituted benzoates (X = 4-MeO, H and 4-NO 2) with a series of Z-substituted pyridines in 80 mol % H 2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Brønsted-type plots exhibit downward curvature (e.g., β 2 = 0.89 ∼ 0.96 when pK a < 9.5 while β 1 = 0.38 ∼ 0.46 when pK a > 9.5), indicating that the reaction proceeds through a stepwise mechanism with a change in rate-determining step (RDS). The pK a°, defined as the pK a at the center of Brønsted curvature, has been analyzed to be 9.5 regardless of the electronic nature of the substituent X in the benzoyl moiety. Dissection of k N into the microscopic rate constants k 1 and k 2/k -1ratio has revealed that k 1 is governed by the electronic nature of the substituent X but the k 2/k -1 ratio is not. Theoretical calculations also support the argument that the electronic nature of the substituent X in the benzoyl moiety does not influence the k 2/k -1 ratio.
DOI
10.5012/bkcs.2010.31.9.2593
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자연과학대학 > 화학·나노과학전공 > Journal papers
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