• 대한화학회지
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• 제34권3호
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• pp.239-247
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• 1990

기체상 $S_N2$ 반응의 형태는 중성 2분자반응, 용매화반응, 이온반응 등으로 나눌 수 있으며, 메카니즘적으로 중성 2분자 반응은 retention 생성물을 만들며 이온반응은 inversion 생성물을 만든다. 한편 용매인 물 한 분자에 의하여 6- 중심 건이상태를 거치는 용매화반응의 경우는 친핵체(또는 이탈기)및 치환기에 의한 전자효과와 입체효과에 따라 두 생성물이 경쟁적으로 만들어진다. 여기에서 얻어진 결과를 이용하여 이온반응의 경우, 중앙 methly group을 매우 bulky 하게 하고 이탈기 능력을 크게 해줌과 동시에 음이온인 친핵체의 하전을 분산시켰을 때 inversion과 retention TS 사이의 에너지 차이가 아주 작게 나타났다. $S_N2$ 반응의 반응중심을 보다 더 큰 2주기 원소로 바꾸었을 때, 5가의 전이상태에 미치는 입체장애가 작아지므로 활성화에너지 장벽이 낮아진다. 반면, 같은 주기에서 원자의 크기가 작아지면 에너지 장벽은 올라간다. B원자의 경우 에너지 장벽이 가장 낮은데, 그것은 C와 N 원자보다도 더 크며 또한 4가의 전이상태를 이루므로 입체장애가 거의 무시되기 때문이다.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1999년도 추계학술발표강연 및 논문개요집
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• pp.76-76
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• 1999

Low resistance ohmic contacts to the Si-doped InGaN(~$\times$10$^{19}$ ㎤) were obtained using the W metallization schemes. Specific contact resistance decreased with increasing annealing temperature. The lowest resistance is obtained after a nitrogen ambient annealing at 95$0^{\circ}C$ for 90s, which results in a specific contact resistance of 2.75$\times$10$^{-8}$ Ω$\textrm{cm}^2$. Interfacial reactions and surface are analyzed using x-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The X-ray diffraction results show that the reactions between the W film and the InGaN produce a $\beta$-W$_2$N phase at the interface. TEM results also show that the $\beta$-W$_2$N has a rough interface, which increase contact area. It shows that the morphology of the contacts is stable up to a temperature as high as 95$0^{\circ}C$. Possible mechanisms are proposed to describe the annealing temperature dependence of the specific contact resistance.

• Bulletin of the Korean Chemical Society
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• 제30권7호
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• pp.1535-1538
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• 2009

We present calculations for $S_N$2/E2 reactions in protic solvents (t-butyl alcohol, ethylene glycol). We focus on the role of the hydroxyl (-OH) groups in determining the $S_N$2/E2 rate constants. We predict that the ion pair E2 mechanism is more favorable than the naked ion E2 reaction in ethylene glycol. E2 barriers are calculated to be much larger (~ 9 kcal/mol) than $S_N$2 reaction barriers in protic solvents, in agreement with the experimental observation [Kim, D. W. et al. J. Am. Chem. Soc. 2006, 128, 16394] of no E2 products in the reaction of CsF in t-butyl alcohol.

• Bulletin of the Korean Chemical Society
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• 제18권8호
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• pp.880-886
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• 1997

Ab initio calculations were carried out on the gas phase acid-catalyzed hydrolysis reactions of sulfinamide using the 3-21G* basis sets. Single point calculations were also performed at the MP2/6-31G* level. The first step in the acid-catalyzed hydrolysis of N-methylmethanesulfinamide, Ⅰ, involves protonation. The most favorable form is the O-protonated one, Ⅱ, which is then transformed into a sulfurane intermediate, Ⅲ, by addition of a water molecule. The reaction proceeds further by an intramolecular proton transfer from O to N (TS2), which is followed by N-S bond cleavage (TS3) leading to the final products. The rate determining step is the N-S bond cleavage (TS3) at the RHF/3-21G* level, whereas it becomes indeterminable at the MP2/6-31G*//3-21G* level of theory. However, the substituent effect studies with N-protonated N-arylmethanesulfinamide, ⅩⅢ, at the MP2/6-31G*//3-21G* level support the N-S bond breaking step as rate limiting.

• 대한화학회지
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• 제23권6호
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• pp.368-373
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• 1979

염화 N,N-이메틸 및 N,N-이에틸카르바모일의 가용매분해반응과 할라이드 교환$(Cl^-,\;Br^-,\;I^-)$반응, 및 염화 N,N-이페닐카르바모일의 가용매분해반응을 속도론적으로 연구하였다. 속도자료와 MO결과로부터 (1) 이 알킬화합물들은$S_N2$ 메카니즘으로, 이페닐화합물은 $S_N1$ 메카니즘으로 반응함을 알았고, (2) 염화이온교환에서는 결합절단이 중요한 반면, $Br^-$ 및 $I^-$ 교환반응에서는 결합 형성이 중요함을 알 수 있었다.

• International Journal of Concrete Structures and Materials
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• 제8권3호
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• pp.213-228
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• 2014

Alkali-activated binder (AAB) is recently being considered as a sustainable alternative to portland cement (PC) due to its low carbon dioxide emission and diversion of industrial wastes and by-products such as fly ash and slag from landfills. In order to comprehend the behavior of AAB, detailed knowledge on relations between microstructure and mechanical properties are important. To address the issue, a new approach to characterize hardened pastes of AAB containing fly ash as well as those containing fly ash and slag was adopted using scanning electron microscopy (SEM) and energy dispersive X-ray spectra microanalyses. The volume stoichiometries of the alkali activation reactions were used to estimate the quantities of the sodium aluminosilicate (N-A-S-H) and calcium silicate hydrate (CSH) produced by these reactions. The 3D plots of Si/Al, Na/Al and Ca/Si atom ratios given by the microanalyses were compared with the estimated quantities of CSH(S) to successfully determine the unique chemical compositions of the N-A-S-H and CSH(S) for ten different AAB at three different curing temperatures using a constrained nonlinear least squares optimization formulation by general algebraic modeling system. The results show that the theoretical and experimental quantities of N-A-S-H and CSH(S) were in close agreement with each other. The $R^2$ values were 0.99 for both alkali-activated fly ash and alkali-activated slag binders.

• 생명과학회지
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• 제16권6호
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• pp.1014-1028
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• 2006

발생기 흰쥐 대뇌피질 발생에 따른 복합당질의 발현 양상 및 이에 미치는 EGEE 영향을 구명하기 위해, 태생 14일, 태생 18일, 생후 수유기 및 이유기와 성제 대뇌를 각 부위로 나누어 복합당질의 당잔기 변화 양상을 9종의 biotinylated lectin(DBA, SBA, PNA, BSL-1, sWGA, RCA-1, UEA-1 Con A 및 LCA)으로 관찰하였다. EGEE 투여시 발생기에 따라 대뇌피질층에 공통적으로 나타나는 렉틴은 Con A 와 LCA 이었고, PNA와 RCA-1은 피질 부위에 따라 부분적으로 나타나 대조군에 비해 결합반응을 보인 렉틴의 수가 감소하였고 DBA, SBA, BSL-1, RCA-1 및 UEA-1은 나타나지 않았다. EGEE 투여시 전 시기에 걸쳐 Con A는 대조군과 유사한 반응을, LCA는 대조군에 비해 태생기, 수유기 및 이유기 때에 반응성이 증가되어 나타났다. 태생기 때 SBA와 sWGA에는 반응성이 나타나지 않았고, PNA는 전두엽피질과 후두엽피질에서 감소하였으며, 두정엽피질과 측두엽피질에서는 반응이 없었다. 수유기 때 PNA는 대조군에 비해 반응이 감소되었고, sWGA에는 반응이 없었으며, 이유기 때에는 sWGA와 PNA에 반응이 나타나지 않았다. 그리고, 성체기 때에는 PNA와 sWGA에 반응이 없었고, Con A에 대해 반응이 감소되었으며, LCA는 전두엽피질와 후두엽피질에서 반응이 감소되었다. 위의 결과로 보아, 환경 호르몬인 EGEE가 대뇌피질의 각 부위에 미치는 영향의 차이는 있지만, 대뇌피질 분화와 성장에 조직병리학적으로 심한 영향을 마치고, 특히 수유기에서 제일 심하였고, 대뇌피질의 $galactosyl-({\beta}-1,3)-N-acetyl-D-galactosamine$, ${\beta}-N-acetyl-D-galactosamine$, ${\beta}-N-acetyl-D-glucosamine$은 감소하고, ${\alpha}-D-mannose$와 ${\alpha}-D-glucose$가 증가하여 이들 당대사에 심한 영향을 미치며, 태생기, 수유기에서 제일 심한 영향을 미쳤다.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.615-621
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• 2013

Solvolyses of isobutyl chloroformate (4) in 43 binary solvent mixtures including highly aqueous media, water, $D_2O$, $CH_3OD$, 2,2,2-trifluoroethanol (TFE) as well as aqueous 1,1,1,3,3,3-hexafluoro-isopropanol (HFIP) solvents were performed at $45^{\circ}C$, in order to further investigate the recent results of D'Souza, M. $J^1$. et al.; solvolyses of 4 are found to be consistent with the proposed mechanism ($Ad_E$). The variety of solvent systems was extended to comprise highly ionizing power solvent media ($Y_{Cl}$ > 2.7 excepted for aqueous fluorinated solvents and pure TFE solvent) to investigate whether a mechanistic change occurs as solvent compositions are varied. However, in case of 18-solvent ranges having aqueous fluorinated solvent systems (TFE-$H_2O$ and HFIP-$H_2O$) and/or having $Y_{Cl}$ > 2.7 solvent systems, the solvent effect on reactivity for those of 4 are evaluated by the multiple regression analysis as competition with $S_N2$ - type mechanism. And in pure TFE and 97 w/w % HFIP solvents with high $Y_{Cl}$ and weak $N_T$, these solvolyses are understood as reactions which proceed through an ionization ($S_N1$) pathway.

• Bulletin of the Korean Chemical Society
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• 제12권3호
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• pp.271-273
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• 1991

Poly (N-vinylcarbazole) was obtained spontaneously by 1,1,2,2-tetracyanocyclopropylstyrene(1) in polar solvents such as dichloromethane and acetonitrile at room temperature. The polymerization reactions were faster in more polar solvent and were not proceeded in less polar solvents such as chloroform and diethyl ether. The formation of poly (N-vinylcarbazole) was explained by bond-forming initiation theory, in which the initiating species are zwitterionic tetramethylene intermediates.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3795-3799
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• 2013

The second-order rate constants ($k_N$) have been measured spectrophotometrically for nucleophilic substitution reactions of Y-substituted-phenyl 2-methylbenzoates (6a-e) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. Comparison of the $k_N$ values for the reactions of 4-nitrophenyl 2-methylbenzoate (6d) with those reported previously for the corresponding reactions of 4-nitrophenyl 2-methoxybenzoate (5) reveals that 6d is significantly less reactive than 5, indicating that modification of 2-MeO in the benzoyl moiety of 5 by 2-Me (i.e., $5{\rightarrow}6d$) causes a significant decrease in reactivity. This supports our previous report that aminolysis of 5 proceeds through a six-membered cyclic intermediate, which is highly stabilized through intramolecular H-bonding interactions. The Br${\o}$nsted-type plot for the reactions of 6d with a series of cyclic secondary amines is linear with ${\beta}_{nuc}=0.71$, which appears to be a lower limit of ${\beta}_{nuc}$ for a stepwise mechanism with breakdown of an intermediate ($T^{\pm}$) being rate-determining step (RDS). The Br${\o}$nsted-type plot for the reactions of 6a-e with piperidine is curved, i.e., the slope of Br${\o}$nsted-type plot (${\beta}_{lg}$) decreases from -1.05 to -0.41 as the leaving-group basicity decreases. The nonlinear Br${\o}$nsted-type plot has been taken as evidence for a stepwise mechanism with a change in RDS (e.g., from the $k_2$ step to the $k_1$ process as the leaving-group basicity decreases). Dissection of $k_N$ into the microscopic rate constants associated with the reactions of 6a-e with piperidine (e.g., $k_1$ and $k_2/k_{-1}$ ratio) also supports the proposed mechanism.