• Bulletin of the Korean Chemical Society
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• 제26권7호
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• pp.1017-1024
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• 2005

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.

• Bulletin of the Korean Chemical Society
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• 제34권4호
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• pp.1030-1034
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• 2013

Elimination reactions of $(E)-2,4-(NO_2)_2C_6H_2CH=NOC_6H_3-2-X-4-NO_2$ (1a-e) promoted by $R_3N/R_3NH^+$ in 70 mol % MeCN(aq) have been studied kinetically. The reactions are second-order and exhibit Br$\ddot{o}$nsted ${\beta}$ = 0.80-0.84 and ${\mid}{\beta}_{lg}{\mid}$ = 0.39-0.42, respectively. For all leaving groups and bases employed in this study, the ${\beta}$ and ${\mid}{\beta}_{lg}{\mid}$ values remained almost the same. The results can be described by a negligible $p_{xy}$ interaction coefficient, $p_{xy}={\partial}{\beta}/pK_{lg}={\partial}{\beta}_{lg}/pK_{BH}{\approx}0$, which describes the interaction between the base catalyst and the leaving group. The negligible pxy interaction coefficient is consistent with the $(E1cb)_{irr}$ mechanism. Change of the base-solvent system from $R_3N$/MeCN to $R_3N/R_3NH^+$-70 mol % MeCN(aq) changed the reaction mechanism from E2 to $(E1cb)_{irr}$. Noteworthy was the relative insensitivity of the transition state structure to the reaction mechanism change.

• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.2143-2147
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• 2014

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.

• Applied Biological Chemistry
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• 제39권1호
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• pp.70-76
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• 1996

일련의 pyridylsulfonyl urea들을 합성하고 25%(v/v) 디옥산 수용액의 넓은 pH범위에서 가수분해 반응속도 상수를 측정하였다. pH-효과, 용매 효과($m{\ll}1,\;n{\ll}3$ 및 ${\mid}m{\mid}{\ll}{\mid}{\ell}{\mid}$), 일반 염기-효과, 산-해리상수(pKa, 3: 4.9 및 5: lit.4.6), 열역학적 활성화 파라미터(${\Delta}H^{\neq}=0.025\;Kcal.mol.^{-1}$ 및 ${\Delta}S^{\neq}=0.54{\sim}\;-2.19\;e.u.$) 및 생성물 분석 결과로부터 반응속도식을 유도하고 가수분해 반응 메카니즘을 제안하였다. 즉, 비(H)치환체, 1-(4,6-dimethoxypyrimidine-2-yl)-3-(2-pyridylsulfonyl) urea, 3은 산성용액에서 A-2형(또는 $A_{AC}2$)반응 그리고 염기성 용액 에서는 $(E_1)_{anion}$ 메카니즘으로 가수분해 반응이 일어난다. 반면에 trifluoromethyl-치환체, 1-(4,6-dimethoxypyrimidine-2-yl)-3-(3-trifluorornethyl-2-pyridylsulfonyl) urea, 5(Flazasulfuron)는 산성 용액중에서 $A-S_N2Ar$형의 반응으로 생성된 conjugate acid($5H^+$), 그리고 pH 9.0 이상에서는 $(E_1)_{anion}$ 및 $(E_1CB)_R$ 반응으로 생성된 conjugate base(CB)를 거쳐 산성 및 염기성 용액중에서 모두 5원자 고리 중간체를 경유하는 Smile 자리옮김 반응으로 산성에서는 3-trifluoromethyl-2-pyridylpyrimidinyl urea(PPU) 그리고 염기성에서는 3-trifluoromethyl-2-pyridyl-4,6-dimethoxy-pyrimidinyl amine(PPA)을 생성하는 가수분해 반응이 일어남을 알았으며 5는 3보다 약 3.5배 빠른 반응속도를 나타내었다.

• Bulletin of the Korean Chemical Society
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• 제21권8호
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• pp.823-827
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• 2000

Gas-Phase reactions of methyl and ethyl nitrites with anionic nucleophiles of SH-, F- and OH- are investigated theoretically at the MP2/6-311+G* level. The SN2 processes are all highly exothermic and proceed with a typ-icaI double-weIl reaction coordinate profile. The elimination reactions of methyl nitrite with SH- and F- are double-well energy surface processes,with stabilizedproduct complexes of NO-...H2S and NO-...HF, pro-ceeding by an E1 cb-like E2 mechanism. The $\beta-elimination$ of ethyl nitrite is an E2 type process. The $\alpha-elimi-nation$ reactions of methyl and ethyl nitrites with OH- have triple-well energy profiles of Elcb pathway with an $\alpha-carbanion$ intermediate which is stabilized bythe vicinal $nc\alpha-{\sigma}*o-N$ charge transfer interactions. CompIex-ation ofmethyl carbanion with HF seems to provide a stable intermediate within a triple-well energy profile of El cb channel in the reaction of F- with methyl nitrite.

• Applied Biological Chemistry
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• 제38권5호
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• pp.455-462
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• 1995

새로운 6종의 제초성, N-(2,6-dimethoxypyrimidin-2-yl)aminocarbonyl-2-치환(Z)-6-(1-hyd roxy-2-fluoroethyl)benzenesulfonamide 유도체(S)를 합성하여 $45^{\circ}C$의 15%(v/v) acetonitrile 수용액속에서 일어나는 가수분해 반응상수를 측정하고 pH-효과, 용매효과, ortho-치환기 효과, 열 역학적 활성화 파라미터(${\Delta}H^{\neq}$및${\Delta}S^{\neq}$) 등의 반응 속도론적인 자료들과 pKa상수(4.80) 및 가수분해 반응 생성물(2-(1-hydroxy-2-fluoroethyl)benzenesulfonamide 및 4,6-dimethoxyaminopyrimidine) 분석 등의 비 반응 속도론적 결과로부터 반응속도식을 유도하고 반응메카니즘을 제안하였다. pH 8.0 이하에서는 일반 산-촉매반응($A-S_E2$)과 특정 산-촉매 반응으로 conjugate acid ($SH^+$)와 사면체 중간체(I)를 경유하는 A-2형(또는 $A_{AC}2$형)반응 그리고 pH 9.0 이상에서는 물 분자가 일반염기(B)로 작용하여 conjugate base (CB)를 경유하는 $(E_1)_{anion}$ 반응으로 진행되는 가수분해 반응 메카니즘을 검토하였으며 pH $7.0{\sim}9.0$사이의 용액중에서는 이들 두 반응이 경쟁적으로 일어남을 알았다.

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.1921-1924
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• 2011

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.

• 대한화학회지
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• 제28권5호
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• pp.328-334
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• 1984

새로운 4가지의 phenyl N-benzenesulfonylchloroformimidate 유도체를 합성하고 $25^{\circ}C$와 1 ; 4 dioxane-물의 이성분 혼합용매중에서 가수분해 반응속도를 자외선 분광 광도법으로 측정하여 넓은 pH범위에 적용되는 가수분해 반응속도식을 유도하였다. 치환기 효과(${\rho}$ = -0.45, ${\rho}$ = 0.40), 용매효과 (m = 1.3-1.5, n = 5.0-5.5), 반응속도식 및 생성물 분석 등의 결과로부터 가수분해 반응 메카니즘을 제안하였다. 즉, pH 0.0-8.0의 산성과 중성용액에서는 $SN_1$, 그리고 pH 10.0이상의 알카리성 용액에서는 $SN_2$반응으로 가수분해가 시작되어 $E_1CB$반응으로 benzensulfonamide를 생성하는 일련의 반응으로 가수분해가 진행됨을 알았다.