• Bulletin of the Korean Chemical Society
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• 제31권12호
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• pp.3543-3548
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• 2010

A kinetic study on nucleophilic displacement reactions of 2-pyridyl X-substituted benzoates 1a-e with potassium ethoxide (EtOK) in anhydrous ethanol is reported. Plots of pseudo-first-order rate constants ($k_{obsd}$) vs. $[EtOK]_o$ exhibit upward curvature. The $k_{obsd}$ value at a fixed $[EtOK]_o$ decreases steeply upon addition of 18-crown-6-ether (18C6) to the reaction mixture up to [18C6]/$[EtOK]_o$ = 1 and then remains nearly constant thereafter. In contrast, $k_{obsd}$ increases sharply upon addition of LiSCN or KSCN. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ has revealed that ion-paired EtOK is more reactive than dissociated $EtO^-$, indicating that $K^+$ ion acts as a Lewis acid catalyst. Hammett plots for the reactions of 1a-e with dissociated $EtO^-$ and ion-paired EtOK result in excellent linear correlation with $\rho$ values of 3.01 and 2.67, respectively. The $k_{EtOK}/k_{EtO^-}$ ratio increases as the substituent X in the benzoyl moiety becomes a stronger electron-donating group. $K^+$ ion has been concluded to catalyze the current reaction by stabilizing the transition state through formation of a 6-membered cyclic complex.

• Bulletin of the Korean Chemical Society
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• 제24권2호
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• pp.193-196
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• 2003

Nucleophilic addition reactions of benzylamines $(XC_6H_4CH_2NH_2)$ to benzylidene Meldrum's acids (BMA; $YC_6H_4CH=C(COO)_2C(CH_3)_2$) have been investigated in acetonitrile at 20.0 ℃. The rates of addition are greatly enhanced due to the abnormally high acidity of Meldrum's acid. The magnitudes of the Hammett $({\rho}_X\;and\;{\rho}_Y)$ and Bronsted $({\rho}_X$)$ coefficients are rather small suggesting an early transition state. The sign and magnitude of the cross-interaction constant, ${\rho}_{XY}$ (= -0.33), and kinetic isotope effects $(k_H/k_D\;{\stackrel}{~}{=}\;1.5-1.7)$ involving deuterated benzylamine nucleophilies $(XC_6H_4CH_2ND_2)$ are indicative of hydrogen-bonded cyclic transition state. The activation parameters, ${\Delta}H^{\neq}\;{\stackrel}{~}{=}\;4\;kcal\;mol^{-1}\;and\;{\Delta}S^{\neq}\;{\stackrel}{~}{=}\;-37\;e.u.$, are also in line with the proposed mechanism.

• 대한화학회지
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• 제58권1호
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• pp.17-24
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• 2014

The oxidative decarboxylation of phenylsulfinylacetic acid (PSAA) by Cr(VI) in 20% acetonitrile -80% water (v/v) medium follows overall second order kinetics, first order each with respect to [PSAA] and [Cr(VI)] at constant [$H^+$] and ionic strength. The reaction is acid catalysed, the order with respect to [$H^+$] is unity and the active oxidizing species is found to be $HCrO_3^+$. The reaction mechanism involves the rate determining nucleophilic attack of sulfur atom of PSAA on chromium of $HCrO_3^+$ forming a sulfonium ion intermediate. The intermediate then undergoes ${\alpha}$,${\beta}$-cleavage leading to the liberation of $CO_2$. The product of the reaction is found to be methyl phenyl sulfone. The operation of substituent effect shows that PSAA containing electron-releasing groups in the meta- and para-positions accelerate the reaction rate while electron withdrawing groups retard the rate. An excellent correlation is found to exist between log $k_2$ and Hammett ${\sigma}$ constants with a negative value of reaction constant. The ${\rho}$ value decreases with increase in temperature evidencing the high reactivity and low selectivity in the case of substituted PSAAs.

• Bulletin of the Korean Chemical Society
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• 제23권10호
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• pp.1459-1462
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• 2002

The kinetics of the addition of X-substituted benzylamines (BA) to Y-substituted Benzylideneacetylacetones (BAA) have been investigated in acetonitrile at $25.0^{\circ}C$. The reaction is studied under pseudo-first-order conditions by keeping a large excess of BA over BAA. The addition of BA to BAA occurs in a single step in which the addition of BA to $C_\alpha$ of BAA and proton transfer from BA to $C_\beta$ of BAA take place concurrently with a four-membered cyclic transition state structure. The magnitude of the Hammett ($p_X$) and Bronsted ($\beta_x$) coefficients are rather small suggesting an early tansition state (TS). The sign and magnitude of the cross-interaction constant, $p_{XY}$ (= -0.49), is comparatible to those found in the normal bond formation processes in the $S_N2$ and addition reactions. The normal kinetic isotope effect ($K_H/K_D$ > 1.0) and relatively low $\Delta$H^{${\neq}$}$ and large negative $\Delta$S^{${\neq}$}$ values are also consistent with the mechanism proposed.

• Bulletin of the Korean Chemical Society
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• 제26권6호
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• pp.935-938
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• 2005

Nucleophilic addition reactions of benzylamines (BA; $XC_6H_4CH_2NH_2$) to $\alpha-cyano-\beta$-phenylacrylamides (CPA; $YC_6H_4CH=C(CN)CONH_2$) have been investigated in acetonitrile at 25.0 ${^{\circ}C}$. The rate is first order with respect to BA and CPA and no base catalysis is observed. The addition of BA to CPA occurs in a single step in which the addition of BA to $C_{\beta}$ of CPA and proton transfer from BA to $C_{\alpha}$ of CPA take place concurrently with a four-membered cyclic transition state structure. The magnitude of the Hammett ($\rho_X$) and Bronsted ($\beta_X$) coefficients are rather small suggesting an early tansition state (TS). The sign and magnitude of the crossinteraction constant, $\rho_XY$ (= −D0.26), is comparable to those found in the normal bond formation processes in the $S_N2$ and addition reactions. The normal kinetic isotope effect ($k_H/k_D\;{\gt}$ 1.0) and relatively low ${\Delta}H^{\neq}$ and large negative ${\Delta}S^{\neq}$ values are also consistent with the mechanism proposed.

• 대한화학회지
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• 제19권6호
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• pp.449-453
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• 1975

Benzyl arenesulfonate와 디메틸아닐린을 아세톤 중에서 $35^{\circ}C$로 반응시켜 離脫基의 置換基效果를 硏究한 結果 다음과 같은 結論을 얻었다. (1) 親核試藥이 피리딘에서 N,N-디메틸아닐린으로 바뀌어도 離脫基의 치환기效果는 변화가 없다. (2) p-MeO의 치환기정수는 아세톤에서 -0.35가 적당했다. (3) 치환 디메틸아닐린의 ) 親核力이 弱할 수록 전이상태에서는 N에서 C로 電子移動이 보다 크며 C${\ldots}$O結合 開裂은 보다 진행된 상태라고 생각된다.

• 대한화학회지
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• 제11권4호
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• pp.170-172
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• 1967

2-Phenyl-5-substituted phenyltetrazole and 2-substituted phenyl-5-phenyltetrazole were prepared from the corresponding hydrazone and phenyl azide with 2-methoxyethanol and metallic sodium as reaction medium at 110~115 $^{\circ}C$. At this reaction condition, however, the preparation of 2-substituted phenyl-5-phenyltetrazoles with substituents of relatively high Hammett substituent constant was unsuccessful. Surprisingly it was found that the solvent molecule was exchanged with substituent during the reaction when tried to obtain 2-m-fluorophenyl-5-phenyltetrazole using benzaldehyde m-fluorophenylhydrazone as starting material. Also disscussed the effect of electronic nature of substituents on the formation of 2,5-diphenyltetrazole derivatives.

• Bulletin of the Korean Chemical Society
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• 제25권8호
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• pp.1231-1237
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• 2004

Rate constants for photolytic reactions of p-substituted 2-diazopropiophenones were determined in acetonitrile. The reactions show a comparatively low value of activation energy and activation enthalpy to alkylcarbenes or other arylcarbenes. The transition state corresponds to the step of a new carbonyl bond formation. The high negative ρ -values are shown in Hammett plots. The kinetics results and EPR spectrum are in accord with a phenomenon that occurs in interconversion between singlet and triplet carbenes.

• Bulletin of the Korean Chemical Society
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• 제3권1호
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• pp.13-18
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• 1982

The new substituent constants $({\sigma}^{\ast})$ are calculated from the acidity constants $(pK^{\ast})$ of phenol derivatives in the excited state ($^1L_b$). These substituent constant are applied to the Hammett equations and found good correlation with $pK^{\ast}$ of 2,6-di-tert-butyl phenol, benzamide, nitroaniline, thiophenol, azobenzene, and benzoic acid derivatives. The correlation was much better than that of ground state substituent constants such as ${\sigma},\;{\sigma}^+$, and ${\sigma}^-$. From these results, the new substituent constants $({\sigma}^{\ast})$are proposed to be used for the linear free energy relationship in the $^1({\pi},{\pi}^{\ast})$ excited states of phenyl compounds.

• Bulletin of the Korean Chemical Society
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• 제21권5호
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• pp.477-482
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• 2000

Phenyl group migration within protonated 1,2-diphenyl hydrazines has been studied theoretically using the semi-empirical AM1 method. This reaction proceeds through a 3-membered cyclic transition state and requires high activation energy. In the reactant, there was no resonance stabilization for the moving Z-ring, however, hammett $p_Z^+$ values are large due to the direct involvement of the Z-ring inthe reaction, and the development of a negative charge on the reaction center gives them a posifive value. In the case of the non-moving ring, $p_Y^+$ values are small and negative owing to the smaller positive charge increase in the reaction center. The cross-interaction constant, $p_YZ^+$, was obtained from the activation enthalpies, using the multipe linear regression methdo, and the interaction between two substituents, Y and Z, is examined.