18938-17-5Relevant academic research and scientific papers
Kinetic study on aminolysis of aryl X-substituted-cinnamates in acetonitrile: Differential medium effect determines reactivity and reaction mechanism
Um, Ik-Hwan,Bae, Ae-Ri,Dust, Julian M.
, p. 13 - 19 (2019/01/10)
A kinetic study on nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted-cinnamates (1a-1f) and Y-substituted-phenyl cinnamates (2a-2g) with a series of alicyclic secondary amines in MeCN at 25.0 ± 0.1 °C is reported. The Br?nsted-type pl
Kinetic Study on Nucleophilic Substitution Reactions of O-Phenyl O-Y-substituted-Phenyl Thionocarbonates with 1,8-Diazabicyclo[5.4.0]undec-7-ene in Acetonitrile
Um, Ik-Hwan,Park, Kyoung-Ho
, p. 1169 - 1173 (2017/09/13)
Second-order rate constants (kN) for nucleophilic substitution reactions of O-phenyl O-Y-substituted-phenyl thionocarbonates (4a–4k) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in MeCN at 25.0 ± 0.1°C are reported. The reactivity of 4a–4k decreases as basicity of the leaving group increases except O-2,4-dinitrophenyl O-phenyl thionocarbonate (4a), which is less reactive than O-3,4-dinitrophenyl O-phenyl thionocarbonate (4b) although the former possesses 2 pKa units less basic nucleofuge than the latter. The Br?nsted-type plot for the reactions of 4b–4k is linear with βlg = ?0.50, a typical βlg value for reactions reported to proceed through a concerted mechanism. The Hammett plot correlated with σY? constants for the reactions of 4b–4k results in a better linear correlation than that correlated with σYo constants. Besides, the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρY = 2.12, r = 0.68 and R2 = 0.990, indicating that a negative charge develops partially on the O atom of the leaving group in the rate-determining step (RDS). Thus, the reactions have been concluded to proceed through a forced concerted mechanism. Effects of steric hindrance on reactivity and reaction mechanism are also discussed in detail.
Kinetic study on nucleophilic substitution reactions of aryl diphenylphosphinates with butane-2,3-dione monoximate and aryloxide anions: Reaction mechanism and origin of the α-effect
Um, Ik-Hwan,Han, Jeong-Yoon
, p. 1180 - 1184 (2016/08/12)
A kinetic study is reported for nucleophilic substitution reactions of X-substituted-phenyl diphenylphosphinates (3a-3f) with butane-2,3-dione monoximate (Ox-) and a series of Y-substituted-phenoxide (Y-PhO-) ions in 50 mol % H2O/50 mol % DMSO at 25.0 ± 0.1°C. The reactions of 3a-3f with Ox- and 4-chlorophenoxide (4-ClPhO-) result in linear Br?nsted-type plots with βlg = -0.70 and -0.64, respectively, a typical βlg value for reactions reported previously to proceed through a concerted mechanism. The Br?nsted-type plots for the reactions of 4-chloro-2-nitrophenyl diphenylphosphinate (3a), 4-nitrophenyl diphenylphosphinate (3b), and 4-acetylphenyl diphenylphosphinate (3d) with Y-PhO- are also linear with βnuc = 0.15-0.35. The current reactions have been concluded to proceed through a concerted mechanism in which the bond formation is much less advanced than the bond rupture in the TS on the basis of the βlg and βnuc values. The α-effect observed in this study is very small (i.e., the kOx-/kp-ClPhO- ratio=4.61-43.5) and is independent of the leaving-group basicity. It has been concluded that the α-effect shown by Ox- in the current reactions is mainly due to desolvation of Ox- in the reaction medium (ground-state contribution) rather than stabilization of the transition-state (TS contribution) on the basis of the kinetic results.
Kinetic study on alkaline hydrolysis of Y-substituted phenyl X-substituted benzenesulfonates: Effects of changing nucleophile from azide to hydroxide ion on reactivity and transition-state structure
Moon, Ji-Hyun,Kim, Min-Young,Han, So-Yeop,Um, Ik-Hwan
, p. 1563 - 1568 (2015/08/11)
Second-order rate constants (kOH-) for alkaline hydrolysis of 2,4-dinitrophenyl X-substituted benzenesulfonates (1a-1f) and Y-substituted phenyl 4-nitrobezenesulfonates (2a-2g) have been measured spectrophotometrically. Comparison of kOH/
Kinetic study on alkaline hydrolysis of Y-substituted phenyl picolinates: Effects of modification of nonleaving group from benzoyl to picolinyl on reactivity and reaction mechanism
Kim, Myung-Joo,Kim, Min-Young,Um, Ik-Hwan
, p. 1138 - 1142 (2015/07/15)
Second-order rate constants (kOH-) for alkaline hydrolysis of Y-substituted phenyl picolinates (6a-6i) have been measured spectrophotometrically. A linear Bronsted-type plot is obtained with βlg = -0.34, which is typical for reactions reported previously to proceed through a stepwise mechanism with formation of an addition intermediate being the rate-determining step (RDS). However, σYo constants result in a much poorer Hammett correlation than σY- constants. Furthermore, the Yukawa-Tsuno plot exhibits an excellent linear correlation with ρY = 0.82 and r = 0.72, indicating that a negative charge develops partially on the O atom of the leaving group in the RDS. Thus, the reactions have been concluded to proceed through a forced concerted mechanism with a highly unstable intermediate 7. Comparison of the current kinetic data with those reported previously for the corresponding reactions of Y-substituted phenyl benzoates has revealed that modification of the nonleaving group from benzoyl to picolinyl causes not only an increase in reactivity but also a change in the reaction mechanism (i.e., from a stepwise mechanism to a forced concerted pathway).
Kinetics of the reaction of phenyl picrates with phenoxide ions in water. Concerted or stepwise?
Crampton, Michael R.,Robotham, Ian A.
, p. 1084 - 1089 (2014/01/06)
A kinetic study is reported of the exchange reactions of substituted phenoxide ions with some ring-substituted 2,4,6-trinitrophenyl ethers in water. The βronsted diagrams formed by plotting log k, where k is the second-order rate constant for reaction, ve
Nucleophilic substitution reactions of phenyl y-substituted-phenyl carbonates with butane-2,3-dione monoximate and 4-chlorophenoxide: Origin of the α-effect
Kim, Min-Young,Min, Se-Won,Um, Ik-Hwan
, p. 49 - 53 (2013/08/24)
Second-order rate constants have been measured spectrophotometrically for the reactions of phenyl Ysubstituted- phenyl carbonates 7a-g with butane-2,3-dione monoximate (Ox-) in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The α-nucleophile Ox- is 53-95 times more reactive than the corresponding normalnucleophile 4-ClPhO- toward 7a-g, indicating that the α-effect is operative. The magnitude of the α-effect (e.g., the kOx/k4-ClPhO ratio) is independent of the electronic nature of the substituent Y. The cause of the α- effect for the reactions of 7a-g has been suggested to be ground-state (GS) effect rather than transition-state (TS) stabilization through a six-membered cyclic TS, in which Ox- behaves a general acid/base catalyst. This idea is further supported by the result that OH- exhibits negative deviation from the linear Bronsted-type plot composed of a series of aryloxides, while Ox- deviates positively from the linearity. Differential solvation of the GS of Ox- and 4-ClPhO- has been suggested to be responsible for the α-effect exerted by Ox-.
Alkaline hydrolysis of Y-substituted phenyl phenyl thionocarbonates: Effect of changing electrophilic center from C=O to C=S on reactivity and mechanism
Kim, Song-I,Park, Hey-Ran,Um, Ik-Hwan
, p. 179 - 182 (2011/10/31)
Second-order rate constants (kOH-) have been measured spectrophotometrically for reactions of Y-substituted phenyl phenyl thionocarbonates (4a-i) with OH- in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The ksu
Pitfalls in assessing the α-effect: Reactions of substituted phenyl methanesulfonates with HOO-, OH-, and substituted phenoxides in H2O
Um, Ik-Hwan,Im, Li-Ra,Buncel, Erwin
supporting information; experimental part, p. 8571 - 8577 (2011/03/20)
Toward resolving the current controversy regarding the validity of the α-effect, we have examined the reactions of Y-substituted phenyl methanesulfonates 1a-1l with HOO-, OH-, and Z-substituted phenoxides in the gas phase versus solu
Analysis of linear free-energy relationships combined with activation parameters assigns a concerted mechanism to alkaline hydrolysis of X-substituted phenyl diphenylphosphinates
Um, Ik-Hwan,Han, Jeong-Yoon,Hwang, So-Jeong
supporting information; experimental part, p. 7324 - 7330 (2009/08/07)
A kinetic study is reported for alkaline hydrolysis of X-substituted phenyl diphenylphosphinates (1a-i). The Bronsted-type plot for the reactions of 1a-i is linear over 4.5 pKa units with βlg= -0.49, a typical βlg value for reactions which proceed through a concerted mechanism. The Hammett plots correlated with σo and σ- constants are linear but exhibit many scattered points, while the corresponding Yukawa-Tsuno plot results in excellent linear correlation with ρ= 1.42 and r=0.35. The r value of 0.35 implies that leaving-group departure is partially advanced at the rate-determining step (RDS). A stepwise mechanism, in which departure of the leaving group from an addition intermediate occurs in the RDS, is excluded since the incoming HO - ion is much more basic and a poorer nucleofuge than the leaving aryloxide. A dissociative (DN + AN) mechanism is also ruled out on the basis of the small βlg value. As the substituent X in the leaving group changes from H to 4-NO2 and 3,4-(NO2)2, ΔH≠ decreases from 11.3 kcal mol-1 to 9.7 and 8.7 kcal mol-1, respectively, while ΔS≠ varies from -22.6 cal mol-1 K-1 to -21.4 and -20.2 cal mol-1 K-1, respectively. Analysis of LFERs combined with the activation parameters assigns a concerted mechanism to the current alkaline hydrolysis of 1a-i.
