• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2423-2427
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• 2011

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for nucleophilic substitution reactions of 3,4-dinitrophenyl diphenylphosphinothioate 9 with alkali metal ethoxides (EtOM, M = Li, Na, K) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plot of $k_{obsd}$ vs. [EtOM] is linear for the reaction of 9 with EtOK. However, the plot curves downwardly for those with EtOLi and EtONa while it curves upwardly for the one with EtOK in the presence of 18-crown-6-ether (18C6). Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constant for the reaction with dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that the reactivity increases in the order $k_{EtOLi}$ < $k_{EtONa}$ < $k_{EtO^-}$ ${\approx}$ $k_{EtOK}$ < $k_{EtOK/18C6}$, indicating that the reaction is inhibited by $Li^+$ and $Na^+$ ions but is catalyzed by 18C6-crowned $K^+$ ion. The reactivity order found for the reactions of 9 contrasts to that reported previously for the corresponding reactions of 1, i.e., $k_{EtOLi}$ > $k_{EtONa}$ > $E_{EtOK}$ > $k_{EtO^-}$ ${\approx}$ $k_{EtOK/18C6}$, indicating that the effect of changing the electrophilic center from P=O to P=S on the role of $M^+$ ions is significant. A four-membered cyclic transition-state has been proposed to account for the $M^+$ ion effects found in this study, e.g., the polarizable sulfur atom of the P=S bond in 9 interacts strongly with the soft 18C6-crowned $K^+$ ion while it interacts weakly with the hard $Li^+$ and $Na^+$ ions.

• Journal of the Korean Mathematical Society
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• v.33 no.2
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• pp.235-247
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• 1996

Many numerical computations in science and engineering can only be solved approximately since the available infomation is partial. For instance, for problems defined ona space of functions, information about f is typically provided by few function values, $N(f) = [f(x_1), f(x_2), \ldots, f(x_n)]$. Knwing N(f), the solution is approximated by a numerical method. The error between the true and the approximate solutions can be reduced by acquiring more information. However, this increases the cost. Hence there is a trade-off between the error and the cost.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.519-523
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• 2012

A kinetic study is reported on nucleophilic displacement reactions of benzyl 2-pyridyl carbonate 6 with alkalimetal ethoxides, EtOM (M = Li, Na, and K), in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plots of pseudo-firstorder rate constant $k_{obsd}$ vs. [EtOM] curve upward, a typical phenomenon reported previously for alkaline ethanolysis of esters in which alkali-metal ions behave as a Lewis-acid catalyst. The kobsd value for the reaction of 6 with a fixed EtOK concentration decreases rapidly upon addition of 18-crown-6-ether (18C6), a complexing agent for $K^+$ ion up to [18C6]/[EtOK] = 1.0 and then remains constant thereafter, indicating that the catalytic effect exerted by K+ ion disappears in the presence of excess 18C6. The reactivity of EtOM towards 6 increases in the order $EtO^-$ < EtOLi < EtONa < EtOK, which is contrasting to the reactivity order reported for the corresponding reactions of 2-pyridyl benzoate 4, i.e., $EtO^-$ < EtOK < EtONa < EtOLi. Besides, 6 is 1.7 and 3.5 times more reactive than 4 towards dissociated $EtO^-$ and ion-paired EtOK, respectively. The reactivity difference and the contrasting metal-ion selectivity are discussed in terms of electronic effects and transition-state structures.

• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.1951-1956
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• 2011

A kinetic study is reported on nucleophilic substitution reactions of 4-nitrophenyl nicotinate 5 and isonicotinate 6 with alkali metal ethoxide EtOM (M = K, Na, and Li) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. Plots of pseudo-first-order rate constant $k_{obsd}$ vs. EtOM concentration exhibit upward curvature for the reactions of 5 and 6 with EtOK and EtONa but are almost linear for those with EtOLi. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constant for the reaction with dissociated $EtO^-$ and ion-paired EtOM, respectively) has shown that $k_{EtOK}$ ${\geq}$ $k_{EtONa}$ > $k_{EtO^-}$ but $k_{EtOLi}$ < $k_{EtO^-}$. It has been concluded that $K^+$ and $Na^+$ ions catalyze the reactions by increasing the electrophilicity of the carbonyl carbon atom through formation of a 4-membered cyclic transition state $TS_3$ or $TS_4$. However, $M^+$ ion catalysis has been found to be much less significant for the reactions of 5 and 6 than for the corresponding reactions of 4-nitrophenyl picolinate 4, which was reported to proceed through a 5-membered cyclic transition state $TS_2$. Although 5 and 6 are significantly more reactive than 4-nitrophenyl benzoate 3, the reactions of 5 and 6 result in smaller $k_{EtOK}/k_{EtO^-}$ ratios than those of 3. The electron-withdrawing ability of the nitrogen atom in the acyl moiety of 5 and 6 has been suggested to be responsible for the increase in reactivity and the decrease in the $k_{EtOK}/k_{EtO^-}$ ratio.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2438-2442
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• 2014

A kinetic study is reported for $S_NAr$ reaction of 1-fluoro-2,4-dinitrobenzene (5a) and 1-chloro-2,4-dinitrobenzene (5b) with alkali-metal ethoxides (EtOM, M = Li, Na, K and 18-crown-6-ether complexed K) in anhydrous ethanol. The second-order rate constant increases in the order $k_{EtOLi}$ < $k_{EtO^-}$ < $k_{EtONa}$ < $k_{EtOK}$ < $k_{EtOK/18C6}$ for the reaction of 5a and $k_{EtOLi}$ < $k_{EtONa}$ < $k_{EtO^-$ < $k_{EtOK}$ < $k_{EtOK/18C6}$ for that of 5b. This indicates that $M^+$ ion behaves as a catalyst or an inhibitor depending on the size of $M^+$ ion and the nature of the leaving group ($F^-$ vs. $Cl^-$). Substrate 5a is more reactive than 5b, although the $F^-$ in 5a is ca. $10pK_a$ units more basic than the $Cl^-$ in 5b, indicating that the reaction proceeds through a Meisenheimer complex in which expulsion of the leaving group occurs after the rate-determining step (RDS). $M^+$ ion would catalyze the reaction by increasing either the nucleofugality of the leaving group through a four-membered cyclic transition state or the electrophilicity of the reaction center through a ${\pi}$-complex. However, the enhanced nucleofugality would be ineffective for the current reaction, since expulsion of the leaving group occurs after the RDS. Thus, it has been concluded that $M^+$ ion catalyzes the reaction by increasing the electrophilicity of the reaction center through a ${\pi}$-complex between $M^+$ ion and the ${\pi}$-electrons in the benzene ring.

• Bulletin of the Korean Chemical Society
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• v.31 no.10
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• pp.2929-2933
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• 2010

Pseudo-first-order rate constants ($k_{obsd}$) have been measured for nucleophilic substitution reactions of 2-pyridyl benzoate 5 with alkali metal ethoxides (EtOM, M = Li, Na, K) in anhydrous ethanol. The plots of $k_{obsd}$ vs. $[EtOM]_o$ are curved upwardly but linear in the excess presence of 18-crown-6-ether (18C6) with significant decreased $k_{obsd}$ values in the reaction with EtOK. The $k_{obsd}$ value for the reaction of 5 with a given EtONa concentration decreases steeply upon addition of 15-crown-5-ether (15C5) to the reaction medium up to ca. [15C5]/$[EtONa]_o$ = 1, and remains nearly constant thereafter, indicating that $M^+$ ions catalyze the reaction in the absence of the complexing agents. Dissection $k_{obsd}$ into $k_{EtO^-}$- and $k_{EtOM}$, i.e., the second-order rate constants for the reaction with the dissociated $EtO^-$ and the ion-paired EtOM, respectively has revealed that ion-paired EtOM is 3.2 - 4.6 times more reactive than dissociated $EtO^-$. It has been concluded that $M^+$ ions increase the electrophilicity of the reaction center through a 6-membered cyclic transition state. This idea has been examined from the corresponding reactions of 4-pyridyl benzoate 6, which cannot form such a 6-membered cyclic transition state.

• Journal of the Korean Statistical Society
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• v.23 no.2
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• pp.513-522
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• 1994

A multi-dimensional design is most easily constructed via the amalgamation of one-dimensional component block designs. However, not all sets of component designs are compatible to be amalgamated. The conditions for compatibility are related to the concept of a complete matching in a graph. In this paper, we give sufficient conditions for unequal-replicate designs. Two types of conditions are proposed; one is based on the number of verices adjacent to at least one vertex and the other is ona a degree of vertex, in a bipartite graph. The former is an extension of the sufficient conditions of equal-replicate designs given by Dean an Lewis (1988).

• Journal of the Korean Applied Science and Technology
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• v.24 no.2
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• pp.205-210
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• 2007

In this paper, we describe a study on the relationship between neutral emulsion manufacture and hardening test of films. The hardeners were prepared by condensation of equimolar amounts of trichlorotriazine with benzene- or naphthalene-based amino or oxy acids at 0 to $5^{\circ}C$ and at pH 7, and used as hardening agents for gelatin. The hardening test of neutral emulsion layers was studied at pH 7.0. For example I(R=ONa) had strong hardening properties, I substituted with an aminobenzosulfonate moiety $(R=NHC_6H_4-p-SO_3Me$ where Me = K, Na) was a much weaker gelatin hardener, and when substituted with amino- or oxynaphthalene derivative (II, III) did not harden gelatin at all. Compound with 2 dichlorotriazine groups as IV exhibited hardening properties. The hardener can be used in neutral emulsion layer of film and showed good hardening effect.

• Electronics and Telecommunications Trends
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• v.8 no.3
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• pp.108-126
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• 1993

개방망은 망 접속을 표준화하여 망을 접근하도록 하는 technical interface의 공개측면과 망이 가지고 있는 망서비스를 공개하여 사용자로 하여금 선택적으로 이용할 수 있게 해주는 망서비스 공개 측면을 모두 고려하여 망구조를 실현해야 한다. 통신망은 망의 서비스 유형 및 일반적인 기능에 따라 음성급 전화망, 데이터망, 전용선망, 이동통신망 및 위성망으로 구분할 수 있으며, 이에 대한 망 접속은 각 망별로 또한 분유될 수 있다. 망서비스는 기술의 발전과 망진화에 따른 기술적인 요인, 고도통신 사업의 다양화에 따른 사업자 요구에 의한 요인, 그리고 시장수요 요인에 의해 계속 발전.진화되어지는 동적인 것이다. 개방망구조는 망서비스와 기술적인 접속을 주요 내용으로 하고 있기 때문에 이것도 역시 계속 진화되는 것으로 해석해야 한다. 본고에서는 개방망의 서비스 측면에서 해당교환 시스팀이나 전송시스팀이 제공가능한 서비스들로서 개방망구조의 서비스메뉴로 표현할 수 있는 것들을 각 망에 대해 자세히 파악하고자 한다. 이번 호에서는 그 두번째 내용으로서 데이터급 망과 전용선망에서 개방망 서비스로서 국내 교환시스팀과 미국의 ONA 일환으로 BOC가 제공 가능한 것들을 소개한다.

• Journal of the Korean Institute of Intelligent Systems
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• v.5 no.3
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• pp.52-63
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• 1995

A neuro-fuzzy algorithm is presented for nuclear reactor power control in a pressurized water reactor. Automatic reacotr power control is complicated by the use of control rods because of highly nonlinear dynamics in the axial power shape. Thus, manual shaped controls are usually employed even for the limited capability during the power maneuvers. In an attempt to achieve automatic shape control, a neuro-fuzzy approach is considered because fuzzy algorithms are good at various aspects of operator's knowledge representation while neural networks are efficinet structures capable of learning from experience and adaptation to a changing nuclear core state. In the proposed neuro-fuzzy control scheme, the rule base is formulated based ona multi-input multi-output system and the dynamic back-propagation is used for learning. The neuro-fuzzy powere control algorithm has been tested using simulation fesponses of a Korean standard pressurized water reactor. The results illustrate that the proposed control algorithm would be a parctical strategy for automatic nuclear reactor power control.