• Bulletin of the Korean Chemical Society
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• v.20 no.5
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• pp.573-576
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• 1999

The rate constants and kinetic solvent isotope effects (KSIE, KMeOH/kMeOD) for solvolyses of para-substituted phenylchloroformates in CH3OH, CH3OD, H2O, D2O, 50% D2O-CH3OD were determined at 15.0 and 25.0℃ using conductometric method. Kinetic solvent isotope effects for the solvolyses of para-substituted phenyl chloroformates were 2.39-2.51, 2.21-2.28, and 1.67-1.69 for methanol, 50% aqueous methanol, and water, respectively. The slopes of Hammett plot for solvolysis of para-substituted phenyl chloroformates in methanol, 50% aqueous methanol, and water were 1.49, 1.17 and 0.89, respectively. The Hammett type plot of KSIE, log (KSIE) versus p, can be a useful mechanistic tool for solvolytic reactions. The slopes of such straight lines for para-substituted phenyl chloroformates are almost zero in methanol, 50% aqueous methanol, and water. It was shown that the reaction proceeds via an associative SN2 and/or general base catalysis addition-elimination (SAN) mechanism based on activation parameters, Hammett p values, and slopes of Hammett type plot of KS-IE.

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.911-913
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• 1997

• Bulletin of the Korean Chemical Society
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• v.12 no.3
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• pp.295-301
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• 1991

The nucleophilic substitution reactions of p-substituted benzenesulfonyl chlorides wiht p-substituted anilines were carried out in 1,1,1,3,3,3-hexafluoro-2-propanol and 2-propanol mixtures. The salt effect was observed to be inhibited by the reaction of 1,1,1,3,3,3-hexafluoro-2-propanol with nucleophiles. To investigate the effectiveness of the salt for the nucleophilic substitution reaction the relative salt effect was determined. According to the comparison with the inhibitive salt effect and the substituent effects for the substrates and nucleophiles, the reactions were predicted to be controlled by the salt effect more than substituent effect in HFP-PrOH mixtures.

• Journal of the Korean Chemical Society
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• v.38 no.1
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• pp.21-25
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• 1994

The proton affinities of substituted imidazoles, relevant to the binding of lexitropsins that contain imidazole ring to the base pair (G-C sequence) of minor groove of DNA, are studied with the aid of EHT calculations. It is shown that proton affinity of imidazole substituted at position $\alpha$ to the basic nitrogen is slightly larger than that of imidazole substituted at N for the methylimidazole. Proton affinities of N-substituted imidazoles are found to be larger than those of imidazoles substituted at position ${\alpha}$ for a selected set of the other derivatives. As predicted the proton affinity increases when electron-donating group is attached at position N of imidazole.

• Journal of the Korean Chemical Society
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• v.33 no.4
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• pp.413-418
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• 1989

The rates for the reaction of substituted 2-phenylethyl tosylates with substituted pyridines were measured in acetonitrile and that of 2-PNS with substituted pyridines were investigated in both acetonitrile and methanol. The substitutent effect was accelerated by an electron-donating substituent on both substrate and nucleophile. Results showed that More O'Ferrall and quantum mechanical model of predicting transition state structure suggest the reaction proceeds via an $S_N2$ mechanism, in which bond-breaking is more advanced than bond-formation. Transition state variation predicted with the quantum mechanical model is consistent with the experimental results, whereas the predictions provided by the More O'Ferrall plots is found to be inconsistent in leaving group. In the reaction of 2-PNS, the rate constants in acetonitrile were larger than that in methanol.

• Journal of the Korean Ceramic Society
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• v.21 no.4
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• pp.355-360
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• 1984

The effect of 2% of $P_2O_5$ substituted in gypsum(5 mol% as $HPO_3$) on the early hydration characteristics of $C_3A$ were investigated and then gypsum only and gypsum mixed with $Ca(H_2PO_4)_2$.$H_2O$(2% as $P_2O_5$) were studied separately for comparison. The early hydration reaction of $C_3A$ with each gypsum were examined by measuring the rate of heat libera-tion of hydration with calorimeter and by analysing the hydration products with X-ray diffractometer and differential thermal analyser. It was shown that phosphogypsum substituted with $P_2O_6$ in the crystal lattice accelerated exceedingly the formation of the ettrignite and following hydrated products. However the other gypsum especially gypsum without any phosphate delayed the formation of various hydration products, It was consequently suggested that when phosphogypsum are used as the retarder of cement setting its reta-rding effect for setting of cement is not ascribed to the retardation of ettringite formation.

• Applied Biological Chemistry
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• v.33 no.1
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• pp.43-51
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• 1990

Meat emulsions containing 0, 15, 30 and 45% of soy protein isolate(SPI), Na-caseinate(Na-CN) and their mixtures were prepared in order to determine the effect of these non-meat proteins on the physical properties and their sensory quality in emulsion type sausage. It was found that SPI was better fat stabilizer and better binder than Na-CN. The mixtures of SPI and Na-CN didn't exert any significant effect on emulsion stability. From the texture profile analysis by using Instron two-cycle compression tests, decrease in the substitution levels and increase in the ratio of SPI/Na-CN resulted in a significant increase in the textural values of hardness, adhesiveness, gumminess, chewiness. The finished products showed that the substituted product for 15 % meat protein had higher textural values than the unsubstituted product. The sensory quality evaluated for the final products showed no significant difference between the SPI substituted product for 15 % meat protein and the unsubstituted product. However, all of the substituted products for 15 % meat protein and some of those for 30 % substitution with SPI and 67 % SPI received higher scores than average.

• Archives of Pharmacal Research
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• v.20 no.1
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• pp.53-57
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• 1997

For the purpose of defining the effects of the N-substituted alkyl groups on the anticonvulsant activities of N-Cbz-.alpha.-aminosuccinimides, various (R)- and (S)-N-alkyl substituted N-Cbz-.alpha.-aminosuccinimides (1 and 2) were prepared from the corresponding (R)- and (S)-N-Cbz-aspartic acid by using known reaction and were evaluated the anticonvulsant activies in the MES and PTZ tests, including their neurotoxicities. The most active compound in the MES test was (R)N-Cbz-.alpha.-amino-N-methylsuccinimide (1b) $(ED_{50}=52.5 mg/kg, Pl=3.2)$. And in case of the PTZ test, (R)-N-Cbz-.alpha.-amino-N-ethylsuccinimide (1c) was the most active compound $(ED_{50}/=32.5mg/kg, Pl=3.1)$. The order of anticonvulsant activities of these compounds against the MES test, as judged from the ED_50values for the R series (1), was N-methyl > N-isobutyl > non-substituted > N-ethyl, N-allyl > N-benzyl compound; for the S series (2) N-methyl > N-altyl > non-substituted > N-isobutyl > N-ethyl > N-benzyl compound. The anticonvulsant activities in the PTZ tests of these compounds exhibited somewhat different pattern ; for the R series (1) Nethyl > N-methyl > N-isobutyl> non-substituted > N-allyl > N-benzyl compound in order of decreasing activity; for S series (2) N-ethyl > N-allyl, non-substituted > N-isobutyl > N-methyl > N-benzyl compound in order of decreasing activity.

• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2393-2397
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• 2009

Second-order rate constants ($k_{HOO}$‒) have been measured spectrophotometrically for nucleophilic substitution reactions of Y-substituted phenyl benzenesulfonates (1a-g) with $HOO^-$ ion in $H_2O$ at $25.0\;{\pm}\;0.1\;{^{\circ}C}$. The Br$\phi$nsted-type plot is linear with ${\beta}_{lg}$ = ‒0.73. The Hammett plot correlated with with ${\sigma}^-$ constants results in much better linearity than ${\sigma}^o$ constants, indicating that expulsion of the leaving group occurs in the rate-determining step (RDS) either in a stepwise mechanism or in a concerted pathway. However, a stepwise mechanism in which departure of the leaving group occurs in the RDS has been excluded since $HOO^-$ ion is more basic and a poorer leaving group than the leaving Y-substituted phenoxide ions. Thus, the reactions of 1a-g with $HOO^-$ ion have been concluded to proceed through a concerted mechanism. The $\alpha$-nucleophile $HOO^-$ ion is more reactive than its reference nucleophile $OH^-$ ion although the former is ca. 4 p$K_a$ units less basic than the latter (i.e., the $\alpha$-effect). TS stabilization through intramolecular H-bonding interaction has been suggested to be irresponsible for the $\alpha$-effect shown by $HOO^-$ ion, since the magnitude of the $\alpha$-effect is independent of the electronic nature of substituent Y in the leaving group. GS destabilization through desolvation of $HOO^-$ ion has been concluded to be responsible for the $\alpha$-effect found in the this study.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3253-3257
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• 2012

Second-order rate constants for the reactions of phenyl Y-substituted-phenyl carbonates 5a-g with Z-substituted-phenoxides ($k_{Z-PhO^-}$) have been measured spectrophotometrically in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. 4-Nitrophenyl phenyl carbonate (5e) is up to 235 times more reactive than 4-nitrophenyl benzoate (4e). The Br$\o$nsted-type plot for the reactions of 5e with Z-substituted-phenoxides is linear with ${\beta}_{nuc}=0.54$, which is typical for reactions reported previously to proceed through a concerted mechanism. Hammett plots correlated with ${\sigma}^o$ and ${\sigma}^-$ constants for the reactions of 5a-f with 4-chlorophenoxide exhibit highly scattered points. In contrast, the Yukawa-Tsuno plot results in an excellent linear correlation with ${\rho}_Y=1.51$ and r = 0.52, indicating that the leaving-group departure occurs at the rate-determining step (RDS). A stepwise mechanism, in which leaving-group departure occurs at RDS, has been excluded since the incoming 4-$ClPhO^-$ is more basic and a poorer nucleofuge than the leaving Y-substituted-phenoxides. Thus, the reaction has been concluded to proceed through a concerted mechanism. Our study has shown that the modification of the nonleaving group from benzoyl to phenyloxycarbonyl causes a change in the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway) as well as an increase in the reactivity.