Structure–reactivity correlations in nucleophilic substitution reactions of Y-substituted phenyl X-substituted benzoates with anionic and neutral nucleophiles
作者:Ik-Hwan Um、Ji-Youn Lee、Mizue Fujio、Yuho Tsuno
DOI:10.1039/b607194e
日期:——
A kineticstudy is reported for the reactions of 4-nitrophenyl X-substituted benzoates (1a-1) and Y-substituted phenyl benzoates (2a-1) with two anionic nucleophiles (OH(-) and CN(-)) and three amines (piperidine, hydrazine, and glycylglycine) in 80 mol% H(2)O-20 mol% dimethyl sulfoxide (DMSO) at 25.0 +/- 0.1 degrees C. Each Hammett plot exhibits two intersecting straight lines for the reactions of
Comparison of Aminolysis of 2-Pyridyl and 4-Pyridyl X-Substituted Benzoates in Acetonitrile: Evidence for a Concerted Mechanism Involving a Cyclic Transition State
作者:Ik-Hwan Um、Ae-Ri Bae、Tae-Il Um
DOI:10.1021/jo402629e
日期:2014.2.7
but rather by resonance stabilization of substrates possessing an electron-donating group (EDG) in the benzoyl moiety. The Brønsted-type plots are linear with βnuc = 0.59 ± 0.02, which is typical of reactions reported to proceed through a concerted mechanism. A cyclic transition state (TS), which forces the reaction to proceed through a concerted mechanism, is proposed. The deuterium kinetic isotope
Evidence for a Catalytic Six-Membered Cyclic Transition State in Aminolysis of 4-Nitrophenyl 3,5-Dinitrobenzoate in Acetonitrile: Comparative Brønsted-Type Plot, Entropy of Activation, and Deuterium Kinetic Isotope Effects
作者:Ik-Hwan Um、Min-Young Kim、Ae-Ri Bae、Julian M. Dust、Erwin Buncel
DOI:10.1021/jo502303f
日期:2015.1.2
catalyzed reactions are linear with βnuc = 1.03 and 0.69, respectively. The ΔH⧧ and ΔS⧧ values measured for the catalytic reaction with morpholine are −0.80 kcal/mol and −61.7 cal/(mol K), respectively. The negative ΔH⧧ with a large negative ΔS⧧ suggests that the reaction proceeds through a highly ordered transitionstate (i.e., a six-membered cyclic transitionstate, which includes a second amine molecule
Kinetic Study on Aminolysis of 2-Chloro-4-nitrophenyl X-Substituted-Benzoates in Acetonitrile and in H<sub>2</sub>O Containing 20 mol % DMSO: Effects of Medium and Substituent X on Reactivity and Reaction Mechanism
作者:Ha-Ram Kim、Jung Hwan Yoon、Min-Young Kim、Ik-Hwan Um
DOI:10.1246/bcsj.20140048
日期:2014.8.15
Second-order rate constants for reactions of 2-chloro-4-nitrophenyl X-substituted-benzoates 1a–1j with a series of cyclic secondary amines in MeCN have been measured. Comparison of the kinetic results with those reported previously for the corresponding reactions carried out in H2O containing 20 mol % DMSO has revealed that amines are less reactive in MeCN. The Brønsted-type plot for the aminolysis of 2-chloro-4-nitrophenyl benzoate (1f) in MeCN is linear with βnuc = 0.64, which is in contrast to the curved Brønsted-type plot reported for the reaction performed in the H2O–DMSO misxture. The Hammett plot for the reactions of 1a–1j with piperidine consists of two intersecting straight lines while the Yukawa–Tsuno plot exhibits an excellent linear correlation with ρX = 1.22 and r = 0.60, indicating that the nonlinear Hammett plot is not due to a change in rate-determining step but is caused by stabilization of substrates possessing an electron-donating substituent through resonance interactions between the substituent and the carbonyl functionality. It has been concluded that medium change from the H2O–DMSO mixture to MeCN forces the aminolysis of 1a–1j to proceed through a concerted mechanism by destabilizing the zwitterionic tetrahedral intermediate (T±).
Kinetic Study on Aminolysis of Y-Substituted-Phenyl X-Substituted-Benzoates: Effects of Substituents X and Y on Reactivity and Reaction Mechanism
作者:Seong Hoon Jeon、Hyun Soo Kim、Young Joon Han、Min-Young Kim、Ik-Hwan Um
DOI:10.5012/bkcs.2014.35.2.471
日期:2014.2.20
A kineticstudy on aminolysis of 2-chloro-4-nitrophenyl X-substituted-benzoates (2a-k) in 80 mol % H2O/20 mol % DMSO at 25.0 o C is reported. The Bronsted-type plot for the reactions of 2-chloro-4-nitrophenyl benzoate (2g) with a series of cyclic secondary amines curves downward (e.g., 1 = 0.25, 2 = 0.85 and pKa o = 10.3), which is typical of reactions reported to proceed through a stepwise mechanism
报告了 2-氯-4-硝基苯基 X-取代苯甲酸酯 (2a-k) 在 80 mol% H2O/20 mol% DMSO 中在 25.0 o C 中氨解的动力学研究。苯甲酸 2-氯-4-硝基苯酯 (2g) 与一系列环状仲胺反应的布朗斯台德型曲线向下(例如,1 = 0.25、2 = 0.85 和 pKa o = 10.3),即据报道,典型的反应是通过逐步机制进行的,其中速率决定步骤 (RDS) 发生了变化。2a-k 与哌啶反应的 Hammett 图由两条相交的直线组成,而相应的 Yukawa-Tsuno 图表现出极好的线性相关性,X = 1.15 和 r = 0.59。因此,已经得出结论,非线性哈米特图不是由于 RDS 的变化,而是由给电子取代基和 C=O 键之间的共振相互作用使底物稳定引起的。在离去芳氧基的 2 位具有取代基的底物与 Y 取代苯甲酸苯甲酸酯 (3ai) 反应的弯曲布朗斯台德型图负偏差,这意味着在