- Aminolysis of 2,4-dinitrophenyl X-substituted benzoates and Y-substituted phenyl benzoates in MeCN: Effect of the reaction medium on rate and mechanism
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Second-order rate constants (kN) have been determined spectrophotometrically for the reactions of 2,4-di-nitrophenyl X-substituted benzoates (1a-f) and Y-substituted phenyl benzoates (2a-h) with a series of alicyclic secondary amines in MeCN at
- Um, Ik-Hwan,Jeon, Sang-Eun,Seok, Jin-Ah
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- Nucleophilic substitution reactions of Y-Substituted-Phenyl Benzoates with Potassium Ethoxide in Anhydrous Ethanol: Reaction Mechanism and Role of K+ Ion
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Pseudo-first-order rate constants (kobsd) have been measured spectrophotometrically for the reactions of Ysubstituted-phenyl benzoates (5a-j) with potassium ethoxide (EtOK) in anhydrous ethanol at 25.0 ± 0.1 °C. The plots of kobsd vs. [EtOK] curve upward regardless of the electronic nature of the substituent Y in the leaving group. Dissection of kobsd into the second-order rate constants for the reactions with the dissociated EtOV and ion-paired EtOK (i.e., kEtO-and kEtOK, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated Et-V. The Bronsted-type plots for the reactions with the dissociated Et-V and ion-paired EtOK exhibit highly scattered points with βlg = -0.5 ± 0.1. The Hammett plots correlated with ao constants result in excellent linear correlations, indicating that no negative charge develops on the O atom of the leaving Ysubstituted-phenoxide ion in transition state. Thus, it has been concluded that the reactions with the dissociated EtOV and ion-paired EtOK proceed through a stepwise mechanism, in which departure of the leaving group occurs after the RDS, and that K+ ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a four-membered cyclic TS structure.
- Kim, Song-I,Cho, Hyo-Jin,Um, Ik-Hwan
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p. 177 - 181
(2014/02/14)
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- Kinetics and mechanism of nucleophilic displacement reactions of Y-substituted phenyl benzoates with cyanide Ion
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Second-order rate constants (kCN-) have been measured for nucleophilic substitution reactions of Y-substituted phenyl benzoates (1a-r) with CN- ion in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot is linear with βlg = -0.49, a typical βlg value for reactions reported to proceed through a concerted mechanism. Hammett plots correlated with σo and σ-constants exhibit many scattered points. In contrast, the Yukawa-Tsuno plot for the same reaction exhibits excellent linearity with pY = 1.37 and r = 0.34, indicating that a negative charge develops partially on the oxygen atom of the leaving aryloxide in the rate-determining step (RDS). Although two different mechanisms are plausible (i.e., a concerted mechanism and a stepwise pathway in which expulsion of the leaving group occurs at the RDS), the reaction has been concluded to proceed through a concerted mechanism on the basis of the magnitude of βlg and pY values.
- Kim, Song-I,Kim, Eun-Hee,Um, Ik-Hwan
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experimental part
p. 689 - 693
(2010/08/19)
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- IMIDAZOLE DERIVATIVE
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A CB2 receptor modulator comprising an imidazole derivative represented by the general formula (I): [wherein, R1 represents optionally substituted lower alkyl or the like; R2 represents optionally substituted cycloalkyl or the like; R3 represents optionally substituted aryl or the like; and n represents an integer of 0 to 3] or a pharmaceutically acceptable salt thereof as an active ingredient, and the like are provided.
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Page/Page column 52
(2009/09/05)
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- Aminolysis of Y-substituted phenyl X-substituted benzoates with piperidine: Effect of nonleaving group substituent
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The title reaction has been suggested to proceed through a zwitterionic tetrahedral intermediate with a change in the rate determining step on the basis of the curved Bronsted-type plots obtained. The curvature center of the curved Bronsted-type plots is at pKa = 6.4 regardless of the electronic nature of the substituent X in the benzoyl moiety.
- Um, Ik-Hwan,Lee, Ji-Youn,Ko, Seung-Hak,Bae, Sun-Kun
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p. 5800 - 5803
(2007/10/03)
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- Structure-reactivity correlations in nucleophilic substitution reactions of Y-substituted phenyl X-substituted benzoates with anionic and neutral nucleophiles
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A kinetic study is reported for the reactions of 4-nitrophenyl X-substituted benzoates (1a-l) and Y-substituted phenyl benzoates (2a-l) with two anionic nucleophiles (OH- and CN-) and three amines (piperidine, hydrazine, and glycylglycine) in 80 mol% H2O-20 mol% dimethyl sulfoxide (DMSO) at 25.0 ± 0.1 °C. Each Hammett plot exhibits two intersecting straight lines for the reactions of 1a-l with the anionic nucleophiles and piperidine, while the Yukawa-Tsuno plots for the same reactions are linear. The Hammett plots for the reactions of 2a-l with hydrazine and glycylglycine demonstrate much better linear correlations with σ- constants than with σ° or σ constants, indicating that the leaving group departure occurs at the rate determining step (RDS). On the contrary, σ- constants result in poorer Hammett correlation than σ° constants for the corresponding reactions with OH- and CN-, indicating that the leaving group departure occurs after the RDS for the reactions with the anionic nucleophiles. The large ρX value (1.7 ± 0.1) obtained for the reactions of 1a-l with the anionic nucleophiles supports the proposal that the reactions proceed through an addition intermediate with its formation being the RDS. The Royal Society of Chemistry 2006.
- Um, Ik-Hwan,Lee, Ji-Youn,Fujio, Mizue,Tsuno, Yuho
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p. 2979 - 2985
(2008/02/11)
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