• Bulletin of the Korean Chemical Society
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• 제33권1호
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• pp.270-274
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• 2012

The nucleophilic substitution reactions of 1,2-phenylene phosphorochloridate (1c) with X-pyridines are investigated kinetically in acetonitrile at $-25.0^{\circ}C$. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. The pyridinolysis rate of 1c with a cyclic five-membered ring is $2.70{\times}10^5$ times faster than its acyclic counterpart (1a: phenyl ethyl chlorophosphate) because of great positive value of the entropy of activation of 1c (${\Delta}S^{\neq}$ = +26 eu) compared to negative value of 1a (${\Delta}S^{\neq}$= -24 eu) over considerably unfavorable enthalpy of activation of 1c (${\Delta}H^{\neq}=20.5kcal\;mol^{-1}$) compared to 1a (${\Delta}H^{\neq}=12.7kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed on the basis of greater selectivity parameters (${\rho}_X$ = -1.99 and ${\beta}_X$ = 0.41) with the strongly basic pyridines compared to those (${\rho}_X$ = -0.42 and ${\beta}_X$ = 0.07) with the weakly basic pyridines.

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4347-4351
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• 2011

The nucleophilic substitution reactions of ethylene phosphorochloridate (2) with X-pyridines are investigated kinetically in acetonitrile at $-20.0^{\circ}C$. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. Unusual positive ${\rho}_X$ (= +2.49) and negative ${\beta}_X$ (= -0.41) values are obtained with the weakly basic pyridines, and rationalized by the isokinetic relationship with isokinetic temperature at $t_{ISOKINETIC}=6.6^{\circ}C$. The pyridinolysis rate of 2 with a cyclic five-membered ring is forty thousand times faster than its acyclic counterpart (3: diethyl chlorophosphate) because of great positive value of the entropy of activation of 2 (${\Delta}S^{\neq}$ = +49.2 eu) compared to negative value of 3 (${\Delta}S^{\neq}$ = -44.1 eu) over considerably unfavorable enthalpy of activation of 2 (${\Delta}H^{\neq}=28.4\;kcal\;mol^{-1}$) compared to 3 (${\Delta}H^{\neq}=6.3\;kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.1037-1041
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• 2012

The nucleophilic substitution reactions of (2R,4R,5S)-(+)-2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine 2-sulfide (3) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $5.0^{\circ}C$. The anilinolysis rate of 3 involving a cyclic five-membered ring is considerably fast because of small negative value of the entropy of activation (${\Delta}S^\neq=-2cal\;mol^{-1}\;K^{-1}$) over considerably unfavorable enthalpy of activation (${\Delta}H^\neq=18.0\;kcal\;mol^{-1}$). Great enthalpy and small negative entropy of activation are ascribed to sterically congested transition state (TS) and bulk solvent structure breaking in the TS. A concerted $S_N2$ mechanism with a backside nucleophilic attack is proposed on the basis of the secondary inverse deuterium kinetic isotope effects, $k_H/k_D$ < 1.

• 한국의류산업학회지
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• 제10권3호
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• pp.394-398
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• 2008

One of barely water soluble ketones, acetophenone (AP) was dissolved in methanol and then was mixed with aqueous solution of C. I. Red Acid 114. In order to find out the role of AP in the dyeing process the rate constants and the activation parameters were calculated. The rate for the dyeing with AP was faster than that without it. Because of the reduced temperature dependence by AP the activation energy ($E_a$) for the dyeing with AP was smaller than that without it. With increasing temperature the activation enthalpy (${\Delta}H^*$), the activation entropy (${\Delta}S^*$), and the activation free energy ($G^*$) decreased, which was more noticeable in dyeing with AP. The rate constants and the activation parameters agreed well with the results from the previous reports that the ability of AP to increase disaggregation of dye molecules, loosening the wool fiber, and wickabilty of dyeing solution made it possible to dye wool fiber at low temperature.

• Bulletin of the Korean Chemical Society
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• 제10권1호
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• pp.50-57
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• 1989

A pressure effect of the dehydrogenation of ethylalcohol catalyzed by alcoholdehydrogenase was observed in Tris-HCl buffer, pH 8.8 from $25^{\circ}C$ to $35^{\circ}C$ under high pressure system by using our new theory. The theory makes it possible for us to obtain all rate and equilibrium constants for each step of all enzymatic reaction with a single intermediate. We had enthalpy and volume profiles of the dehydrogenation to suggest a detail and reasonable mechanism of the reaction. In these profiles, both enthalpy and entropy of the reaction are positive and their values decrease with enhancing pressure. It means that the first step is endothermic reaction, and its strength decrease with elevating pressure. At the same time, all activation entropies have large negative values, which prove that not only a ternary complex has a more ordered structure at transition state, but also water molecules make a iceberg close by the activated complex. In addition to this fact, the first and second step equilibrium states are controlled by enthalpy. The first step kinetic state is controlled by enthalpy but the second step kinetic state is controlled by entropy.

• 한국수소및신에너지학회논문집
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• 제9권3호
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• pp.127-133
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• 1998

각각 다른 기판온도에서 진공 증착법으로 제작된 Pd 박막들의(두께 ) 수소 흡수-방출 동역학을 실험하였다. 상, 온도영역에서 수소기체를 흡수-방출 시키면서 정방향과 역방향 활성화에너지를 구하고 반응엔탈피를 구하였다. 기판의 온도가 상온인 시료는 정반응 활성화에너지가 kcal/mol H이고 역방향은 kcal/mol H 반응엔탈피는 -2kcal/mol H였다. 기판의 온도가 인 시료는 정방향 활성화에너지 kcal/mol H 이고 역방향 활성화에너지 kcal/mol H였다. 기판의 온도가 상온인 시료의 구조적 치밀성, 온도변화에 따른 비저항 값의 변화율 등을 측정해 보았을 때 기판의 온도가 상온인 시료에 비하여 더 안정된 상태였지만 활성화 에너지의 오차값이 크게 얻어졌다.

• 대한화학회지
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• 제35권1호
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• pp.64-69
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• 1991

아세토니트릴 용매 중에서 p-methylphenacyl arenesulfonate와 피리딘의 반응을 1∼2000 bars 및 35∼55$^{\circ}C$에서 전기전도도법으로 측정하였다. 반응속도는 온도와 압력의 증가에 따라 증가하였으며, 이탈기에 전자받개 치환기가 도입됨에 따라 증가하였다. 활성화엔탄피, 엔트로피 및 부피로부터 이 반응은 전반적으로 S$_N$2 반응으로 진행되나 압력이 증가함에 따라 C${\cdots}$O 결합분열이 더욱 진전된 dissociative S$_N$2 반응으로 진행됨을 알 수 있었다.

• 대한화학회지
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• 제21권5호
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• pp.339-352
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• 1977

소성변형에 대한 저자들의 이론(제1보)을 요업재료, 금속, 합금 및 단결정들에 적용하였다. 그 결과 다중 결정에서는 dislocation 운동과 grain boundary 운동이 실험조건에 따라 함께 또는 분리되어 나타나는 반면 단결정에서는 dislocation 운동만 나타났다. 유동식에 나타나는 파라미터$({\alpha}_{d1},\;1/{\beta}_{d1})와\;({\alpha}_{gj}/X_{gj},\;1/{\beta}_{gj})$ (j = 1 or 2) 및 활성화엔탈피 ${\Delta}H_{k1}^{\neq}$ (k = d 혹은 g)를 구하여 예측한 소성변형은 실험과 잘 일치함을 보았다. 여기서 첨자 d1는 첫번째의 dislocation 유동단위, gj는 j번째 grain boundary 유동단위를 나타낸다. 활성화엔탈피에 대하여 ${\Delta}H_{d1}^{\neq}$는 bulk의 자체확산에 대한 활성화엔탈피와 일치하고 ${\Delta}H_{g1}^{\neq}$는 grain boundary 자체확산에 대한 활성화엔탈피와 일치하였다. 이 사실은 저자들의 이론의 정당성을 보이고 있다.

• 한국염색가공학회지
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• 제14권1호
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• pp.51-57
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• 2002

In the prior study, the mechanical properties and the dyeability of the easily dyeable polyester grim(EDY) were investigated. In this study, to interpret the dyeing behavior of EDY with C. I. Disperse Violet 1, the thermodynamic parameters of dyeing, such as the standard affinity, the heat of dyeing(the enthalpy change), the entropy change, the diffusion coefficient, and the activation energy of diffusion, were obtained from adsorption isotherms and dyeing rate at various temperatures and compared to these of regular polyester (REG-PET). The heat of dyeing(the enthalpy change) and the entropy change for EDY showed smaller negative values than those for REG-PET. This means that the dye molecules in the EDY are combined more loosely than in the REG-PET and that is due to the flexibility of polymer chains of EDY. The diffusion coefficients of C. I. Disperse Violet 1 into the EDY were larger than those for REG-PET, and the activation energy of diffusion on EDY was smaller than that on REG-PET.

• 한국수산과학회지
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• 제24권5호
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• pp.340-344
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• 1991

각종 어육의 동결 및 가열과정 중의 이화학적 품질변화의 규명하고 저온저장 및 가열조건의 확립과 장치의 설계를 위하여 필요로하는 열물성과 변성온도를 DSC를 이용 측정함으로서 다음의 결과를 얻었다. 1. 어육의 발열반응개시온도는 냉각속도가 증가할수록 강하하였으며, 활성화에너지, 엔탈피 및 엔트로피는 냉각속도의 증가와는 상반되는 경향을 보였다. 동결잠열은 냉각속도에 관계없이 거의 -정한 값을 나타내었다. 2. 어육의 동결과정 중의 자유에너지의 변화는 냉각속도와 조성성분의 영향보다는 온도에 의한 영향이 큰 것으로 나타났다. 3. 어육속의 지질 및 단백질의 변성온도는 가열속도와 상관관계를 나타내었으며, 지질의 함양이 많을수록 변성온도가 낮게 나타났다. 변성엔탈피는 각각 0.04-0.13, 0.07-0.17cal/g 값을 얻었다.