http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Pyun Sang Yong,Paik Kyu Cheol,Han Man So,Cho Bong Rae 대한화학회 2021 Bulletin of the Korean Chemical Society Vol.42 No.7
Reactions of 4-nitrophenyl 2-furoates (1a–e) with R2NH/R2NH2 + in 20 mol% DMSO(aq) have been studied. The reactions produced aminolysis products and exhibited second-order kinetics. The Brönsted plots were linear with βnuc values of 0.75–0.89, which remained nearly the same for all 5-furyl substituents. The rate data showed excellent correlations on the Yukawa-Tsuno plots with ρ(x) = 0.72–1.1, and r = 0.55–0.95, respectively. The ρ value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the C O bond and a decrease in the resonance contribution. The results have been interpreted with the addition–elimination mechanism in which the second step is the rds. By comparing with the data for ArC(O)OC6H4-4-NO2 (Ar = Ph, thienyl), the effect of the aryl group on the acyl transfer reaction was assessed.
Kinetics Studies on the Mechanism of Hydrolysis of S-Phenyl-S-vinyl-N-p-tosylsulfilimine Derivatives
Pyun, Sang-Yong,Kim, Tae-Rin,Lee, Chong-Ryoul,Kim, Whan-Gi Korean Chemical Society 2003 Bulletin of the Korean Chemical Society Vol.24 No.3
Hydrolysis reactions of S-phenyl-S-vinyl-N-p-tosylsulfilimine (VSI) and its derivatives at various pH have been investigated kinetically. The hydrolysis reactions produced phenylvinylsulfoxide and p-toluene sulfonamide as the products. The reactions are first order and Hammett ρ values for pH 1.0, 6.0, and 11.0 are 0.82, 0.45, and 0.57, respectively. This reaction is not catalyzed by general base. The plot of k vs pH shows that there are three different regions of the rate constants $(k_t)$ in the profile.; At pH < 2 and pH > 10, the rate constants are directly proportional to the concentrations of hydronium and hydroxide ion catalyzed reactions, respectively. The rate constant remains nearly the same at 2 < pH < 10. On the bases of these results, the plausible hydrolysis mechanism and a rate equation have been proposed: At pH < 2.0, the reaction proceeds via the addition of water molecule to sulfur after protonation at the nitrogen atom of the sulfilimine, whereas at pH > 10.0, the reaction proceeds by the addition of hydroxide ion to sulfur directly. In the range of pH 2.0-10.0, the addition of water to sulfur of sulfilimine appears to be the rate controlling step.
Pyun, Sang-Yong,Cho, Bong-Rae Korean Chemical Society 2005 Bulletin of the Korean Chemical Society Vol.26 No.7
Elimination reactions of $XC_6H_4CH_2CO_2C_6H_3-2-Y-4-NO_2$ have been studied under various conditions. When X was moderately electron-withdrawing, Y = H, and base-solvent was $R_2$NH-MeCN, the reaction proceeded by the E2 mechanism via an E1cb-like transition state. Concave downward curve was noted in the Hammett plots. When X = 4-$NO_2$, Y = Cl, $CF_3,\;NO_2$, and the base-solvent was ${R_2NH/R_2NH_2}^+$ in 70 mol % MeCN(aq), the reaction proceeded by the E2 mechanism. The mechanism changed to a competing E2 and E1cb when X = 4-$NO_2$ and Y = H, MeO, and to the E1cb when X = 2,4-($NO_2)_2$, and Y = $NO_2$. From these results, a plausible pathway of the change of the mechanism from E2 to the E1cb extreme is proposed.
Group-Based Channel Access Scheme for a V2I Communication System using Smart Antenna
Sung-Yeop Pyun,Widiarti, Helena,Yong-Jin Kwon,Jong-Wuk Son,Dong-Ho Cho IEEE 2011 IEEE Communications Letters Vol.15 No.8
<P>We propose a vehicle-to-infrastructure (V2I) communication system that utilizes a smart antenna technology to increase service coverage and system throughput. During contention-based channel access, a collision occurs when more than one vehicle selects the same minislot to transmit an access signal to an infrastructure. To solve this problem, we propose a group-based channel access scheme. Numerical analysis and simulation results show that the proposed scheme can help to reduce the number of collisions that occur during channel access.</P>
Pyun, Sang-Yong,Byun, Woong-Sub,Cho, Bong-Rae Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.6
Nitrile-forming eliminations from $(E)-2,4,6-(NO_2)_3C_6H_2CH=NOC_6H_4-2-X-4-NO_2$ (1) promoted by $R_3NH/R_3NH^+$ in 70 mol % MeCN(aq) have been studied kinetically. When X = $NO_2$, the reactions exhibited second-order kinetics as well as Br$\"{o}$nsted ${\beta}$ = 0.63 and ${\mid}{\beta}_{lg}{\mid}$ = 0.34-0.46, and an E2 mechanism is evident. As the leaving group was made poorer (X = H, Cl, and $CF_3$), Br$\"{o}$nsted ${\beta}$ value increased from 0.63 to 0.85-0.89 without much change in the ${\mid}{\beta}_{lg}{\mid}$ value E2, indicating that structure of the transition state changed to an E1cb-like with extensive $C_{\beta}-H$ bond cleavage, significant negative charge development at the ${\beta}$-carbon, and limited $C_{\alpha}$-OAr bond cleavage.
Pyun, Sang Yong,Kim, Ju Chang,Cho, Bong Rae Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.7
Ketene-forming elimination from 2-X-4-nitrophenyl furylacetates (1a-d) promoted by $R_2NH-R_2NH_2{^+}$ in 70 mol % MeCN(aq) has been studied kinetically. When X = Cl and $NO_2$, the reactions exhibited second-order kinetics as well as Br$\ddot{o}$nsted ${\beta}$ = 0.37-0.54 and $|{\beta}_{lg}|$ = 0.31-0.45. The Br$\ddot{o}$nsted ${\beta}$ decreased with a poorer leaving group and $|{\beta}_{lg}|$ increased with a weaker base. The results are consistent with an E2 mechanism. When the leaving group was changed to a poorer one [X= H (1a) and $OCH_3$ (1b)], the reaction mechanism changed to the competing E2 and E1cb mechanisms. A further change to the E1cb mechanism was realized for the reaction of 1a with $i-Pr_2NH/i-Pr_2NH_2{^+}$ in 70 mol % MeCN-30 mol % $D_2O$. By comparing the kinetic results in this study with the existing data for $ArCH_2C(O)OC_6H_3-2-X-4-NO_2$, the effect of the ${\beta}$-aryl group on the ketene-forming elimination was assessed.
Pyun, Sang Yong,Cho, Bong Rae Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.7
Reactions of 4-nitrophenyl 2-thiophenecarboxylate (1a-e) with $R_2NH/R_2NH{_2}^+$ in 20 mol % DMSO (aq) have been studied kinetically. The $2^{nd}$ order kinetics, ${\beta}_{nuc}$ = 0.88-0.98, and linear Hammett and Yukawa-Tsuno plots observed for these reactions indicate an addition-elimination mechanism in which the $2^{nd}$ step is rate limiting. The ${\beta}_{nuc}$ value increased with a stronger electron-withdrawing 5-thienyl substituent, the Hammett plots are linear except for X = MeO, and Yukawa-Tsuno plots are linear with ${\rho}$ = 0.79-1.32 and r = 0.28-0.93, respectively. The ${\rho}$ value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the C=O bond and a decrease in the resonance demand. These results have been interpreted with enhanced N-C bond formation in the transition state with the reactivity increase.