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문지현,김민영,한소엽,엄익환 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.6
Second-order rate constants () 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 with the values reported previously for the corresponding reactions with has revealed that OH is only 103-fold more reactive than , although the former is 11 pK a units more basic than the latter. The Yukawa–Tsuno plot for the reactions of 1a–1f results in an excellent linear correlation with ρ X = 2.09 and r = 0.41. The Brønsted-type plot for the reactions of 2a–2g is linear with β lg = −0.51, which is typical for reactions reported to proceed through a concerted mechanism. The Yukawa–Tsuno plot for the reactions of 2a–2g exhibits excellent linearity with ρ Y = 1.85 and r = 0.25, indicating that a partial negative charge develops on the O atom of the leaving group in the transition state. Thus, the alkaline hydrolysis of 1a–1f and 2a–2g has been concluded to proceed through a concerted mechanism. Comparison of the ρ X and β lg values for the reactions with ions suggests that the reactions with hydroxide ion proceed through a tighter transition-state structure than those with azide ion.
서현욱,김민영,한소엽,엄익환 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.7
Second-order rate constants (kN3−) for SNAr reactions of 1-(Y-substituted-phenoxy)-2,4-dinitrobenzenes (2a–2h) with N3− in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C have been measured spectrophotometrically. The Brønsted-type plot is linear with βlg = −0.38. The Hammett plots correlated with σYo and σY− constants exhibit highly scattered points. In contrast, the Yukawa–Tsuno plot results in an excellent linear correlation with ρY = 1.02 and r = 0.51, indicating that a negative charge develops partially on the O atom of the leaving Y-substituted-phenoxy moiety in the transition state. Accordingly, the reactions have been concluded to proceed through a stepwise mechanism, in which expulsion of the leaving group occurs in the rate-determining step. Comparison of kN3− with the kOH− values reported previously for the corresponding reactions with OH− has revealed that N3− is only 6- to 26-fold less reactive than OH− toward substrates 2a–2h, although the former is over 11 pKa units less basic than the latter. Solvation and polarizability effects have been suggested to be responsible for the unusual reactivity shown by N3− and OH−. Effects of changing nucleophile from OH− to N3− on reaction mechanism and reactivity are discussed in detail.
문지현,김민영,한소엽,엄익환 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.5
The second-order rate constants for reactions of 2,4-dinitrophenyl X-substituted-benzenesulfonates (4a–4f) and Y-substituted-phenyl-4-nitrobenzenesulfonates (5a–5f) with N 3 − ion have been measured spectrophotometrically. The reactions of 4a–4f proceed through SO and CO bond fission pathways competitively. Fraction of the SO bond fission decreases rapidly as the substituent X in the benzenesulfonyl moiety changes from an electron-withdrawing group to an electron-donating group. The Hammett plots for reactions of 4a–4f are linear with ρX = 1.87 and 0.56 for the SO and CO bond fission, respectively. The fact that the substituent X is further away from the reaction site of the CO bond fission than that of the SO bond fission is one reason for the smaller ρX value. The nature of the reaction mechanism (i.e., a stepwise mechanism in which expulsion of the leaving group occurs after the rate-determining step) is also responsible for the smaller ρX value obtained from the CO bond fission. The Brønsted-type plot for the reactions of 5a–5f is linear with βlg = −0.63, which is typical for reactions reported previously to proceed through a concerted mechanism. Effects of substituents X and Y on regioselectivity and reaction mechanism are discussed in detail.
Punna Reddy Ullapu,구수진,최연희,박지연,한소엽,백두종,이재균,배애님,민선준,조용서 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.8
The synthesis and biological evaluation of 1-heteroarylmethyl 1,4-diazepane derivatives as potential T-type calcium channel blockers is described. In this study, we have identified the compound 21i exhibiting the most potent T-type calcium channel blocking activity with IC_50 value of 0.20 μM, which is superior to that of mibefradil.