• Journal of the Korean Chemical Society
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• v.43 no.1
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• pp.85-91
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• 1999

The second order rate constants for the hydrolysis of substituted phenyl N,N-diethyl-P-benzylphosphonamidates (2,4-$(NO_2)_2$, 4-$NO_2$, 4-CN, 4-Cl, 4-H)in 20% dioxane-water (v/v) have been determined by UV/Vis spectrophotometric method at various temperatures. The activation parameters (Ea, ${\Delta}H^{\neq}$,${\Delta}S^{\neq}$) were calculated from the rate constants and the reaction constant ($\rho$) was also estimated by Hammett equation. The activation entropies of the title reactions show considerably negative values, this result is not consistent with a dissociative mechanism (EA) in which a positive or a slightly negative value of the entropy of activation should be expected. Further, kinetic evidence for an associative mechanism (AE) was obtained from the linear free energy relationship. By the results of kinetic study for the alkaline hydrolysis of substituted phenyl N,N-diethyl-P-benzylphosphonamidates, it may be concluded that these reactions proceed through an associative mechanism.

• Journal of the Korean Chemical Society
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• v.38 no.5
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• pp.391-396
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• 1994

The hydrolysis of $\alpha-benzoxystyrene(1)$ in strong acidic solution has been investigated kinetically. In perchloric acid concentration lower than 5.5 M($H_o$ < -3.0), hydration paramer $\omega$ = + 7.6, and $\Phi$ = + 0.54 were obtained. The solvent isotope effect $k_{H_2O}/K_{D_2O}$ is 0.72. The substituent effect was found to conform to the Hammett $\sigma^+$ constant with $\rho$ = -0.60. On the basis of these results and other evidence, the hydrolysis of the enol ester proceeds by $A_{AL}$2 type mechanism. In concentration greater than 5.5 M($H_o$ > -3.0), isotope effect, $k_{H_2O}/_{D_2O}$ is 3.32, substituent effect, $\rho$ is -1.60 and the rate is linear with the acidity function, $H_o$. Thus, the mechanism changes one involving initial, and rate-determining olefin protonation.

• Bulletin of the Korean Chemical Society
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• v.35 no.7
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• pp.2135-2138
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• 2014

A kinetic study is reported for the SNAr reaction of 1-Y-substituted-phenoxy-2,4-dinitrobenzenes (1a-1h) with OH- in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The second-order rate constant ($k_{OH^-}$) increases as the substituent Y in the leaving group changes from an electron-donating group (EDG) to an electronwithdrawing group (EWG). The Br${\o}$nsted-type plot for the reactions of 1a-1h is linear with ${\beta}_{lg}$ = -0.16, indicating that the reactivity of substrates 1a-1h is little affected by the leaving-group basicity. A linear Br${\o}$nsted-type plot with ${\beta}_{lg}=-0.3{\pm}0.1$ is typical for reactions reported previously to proceed through a stepwise mechanism in which formation of a Meisenheimer complex is the rate-determining step (RDS). The Hammett plot correlated with ${\sigma}_Y{^{\circ}}$ constants results in a much better correlation than that correlated with ${\sigma}_Y{^-}$constants, implyng that no negative charge is developing on the O atom of the leaving group (or expulsion of the leaving group is not advanced at all in the TS). This excludes a possibility that the $S_NAr$ reaction of 1a-1h with $OH^-$ proceeds through a concerted mechanism or via a stepwise pathway with expulsion of the leaving group being the RDS. Thus, the current reactions have been concluded to proceed through a stepwise mechanism in which expulsion of the leaving group occurs rapidly after the RDS.

• Journal of the Korean Chemical Society
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• v.41 no.2
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• pp.69-76
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• 1997

Kinetic studies for the nucleophilic substitution reactions of the benzoic anhydrides with anilines in methanol-acetonitrile mixtures at$35.0{\circ}C$have been carried out in order to elucidate the reaction mechanism. Individual rate constants$k_{XY}$and$k_{XZ}$were decided from the ratios of the reaction products for the competitive substitution reaction at either one of the two carbonyl carbons in benzoic anhydride. Transition state structure and reaction mechanism were elucidated by the Hammett$p_x,\;p_y$and$p_z$values and cross interaction constant$p_x\;p_y$and$p_zvalues. The reaction of the benzoic anhydride has been proposed to proceed by a frontside attack$S_N2 $mechanism with four-membered ring transition state from unusually large magnitude of the$ρ_X,\;ρ_{XY},\;ρ_{XZ}$and positive$p_Y$values.

• Bulletin of the Korean Chemical Society
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• v.31 no.12
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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.

• Journal of the Korean Chemical Society
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• v.19 no.6
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• pp.449-453
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• 1975

Substituent effect of the leaving groups of the reaction of benzyl arenesulfonate with dimethylanilines in acetone at $35^{\circ}C$ was obtained with the following results. 1. Substituent effect of the leaving groups was not variable when changed from pyridine to N,N-dimethylaniline in nucleophile 2.In acetone, the Hammett ${\sigma}$ constant of p-MeO of the leaving group was -0.35. 3. The weaker the nucleophilicity in dimethylaniline, the stronger the movement of electron from N to C, and the cleavage of the C${\ldots}$0 bond in transition state proceeds.

• Journal of the Korean Chemical Society
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• v.11 no.4
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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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• v.25 no.8
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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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• v.3 no.1
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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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• v.21 no.5
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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.