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Effect of o-methyl group on rate, mechanism, and resonance contribution: Aminolysis of Y-substituted phenyl X-substituted 2-methylbenzoates

Title
Effect of o-methyl group on rate, mechanism, and resonance contribution: Aminolysis of Y-substituted phenyl X-substituted 2-methylbenzoates
Authors
Um I.-H.Lee J.-Y.Lee H.W.Nagano Y.Fujio M.Tsuno Y.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2005
Journal Title
Journal of Organic Chemistry
ISSN
0022-3263JCR Link
Citation
vol. 70, no. 13, pp. 4980 - 4987
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
Second-order rate constants have been determined spectrophotometrically for the reactions of 4-nitrophenyl X-substituted 2-methylbenzoates (2a-e) and Y-substituted phenyl 2-methylbenzoates (3a-e) with alicyclic secondary amines in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The o-methyl group in the benzoyl moiety of 2a-e retards the reaction rate but does not influence the reaction mechanism. The Hammett plots for the reactions of 2a-e are nonlinear, while the corresponding Yukawa-Tsuno plots are linear with large r values (1.06-1.70). The linear Yukawa-Tsuno plots suggest that stabilization of the ground-state through resonance interaction between the electron donating substituent X and the carbonyl group is responsible for the nonlinear Hammett plots, while the large r values imply that the ground-state resonance interaction is significant. The reactions of 2a-e resulted in smaller ρX values but larger r values than the corresponding reactions of 4-nitrophenyl X-substituted benzoates (1a-e). The small ρX value for the reactions of 2a-e (e.g., ρX = 0.22) is suggested to be responsible for the large r value (e.g., r = 1.70). The reactions of 3a-e with piperidine are proposed to proceed in a stepwise manner with a change in the rate-determining step on the basis of the curved Brønsted-type plot obtained. Microscopic rate constants associated with the reactions of 3a-e are also consistent with the proposed mechanism. © 2005 American Chemical Society.
DOI
10.1021/jo050172k
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자연과학대학 > 화학·나노과학전공 > Journal papers
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