• The Korean Journal of Food And Nutrition
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• v.5 no.1
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• pp.23-32
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• 1992

Kinetic studies of nucleophilic substitution reactions of dansyl, bansyl, dabsyl chlorides with pyridines have been investigated at $0^{\circ}C$ in a range of methanol-acetonitrile binary solvent mixtures. The order of magnitude for reactivity of substrates with pyridines in the same reaction condition is dabsyl chloride>dansyl chloride> bansyl chloride. The value of $\rho$n(-2.29~ -4.66) and $\beta$(0.537~0.901) associated with a change substituent in the nucleophile are large and indicate a relatively advanced bond formation in the transition state. Solvatochromic correlations were predicted the increase of bond formation transition state according to the increasing MeCN contents, showing the greater contribution of polarity polarizability ($\pi$*) than hydro-gen bond donar acidity($\alpha$). We conclude that the reactions of dansyl, bansyl, dabsyl chlorides with pyridines proceed via associative Sn2 type reaction mechanism.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1353-1354
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• 2006

The dielectric properties of $Ba_{0.5}Sr_{0.5}TiO_3$(BST) and MgO-doped BST ceramics were investigated for tunable microwave applications by sol-gel method. The effects of MgO mixing with BST. It is observed that Mg substitution into BST causes a shift in the cubic-tetragonal BST Phase transition peak to a lower temperature. MgO-substituted BST and MgO-mixed phases exhibit homogeneous and broadened BST phase transition peaks. Mg substitution into BST has a significant effect on the grain sife reduction. Dielectric constant and loss is inhanced with decrease MgO dopant.

• Bulletin of the Korean Chemical Society
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• v.18 no.4
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• pp.390-394
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• 1997

Nucleophilic substitution reactions of 2-thiopheneethyl benzenesulfonates (2-TEB) and 3-thiopheneethyl benzenesulfonates (3-TEB) with anilines and N,N-dimethylanilines (DMA) are investigated in acetonitrile at 60.0 ℃. The cross-interaction constants ρxz determined for the reactions with anilines are large negative (- 0.50) which are comparable to those for the similar predominantly frontside-attack SN2 reactions of 1-phenylethyl (1-PEB), 2-phenylethyl (2-PEB) and cumyl benzenesulfonates. A large negative ρxz value (- 0.4∼- 0.8) is considered to provide a mechanistic criterion for the frontside-attack SN2 mechanism with a four-center transition state. In agreement with this proposal the kinetic isotope effects, kH/kD, involving deuterated aniline nucleophiles are all greater than one reflecting partial N-H(D) bond cleavage in the transition state. The MO theoretical reactant structures of 1-PEB, 2-PEB and 2-TEB based on the PM3 calculation show that the benzene ring blocks the backside nucleophile approach to the reaction center carbon (Cα) enforcing the frontside-attack SN2 mechanism.

• Bulletin of the Korean Chemical Society
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• v.11 no.5
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• pp.435-438
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• 1990

Primary and secondary ${\alpha}$-deuterium kinetic isotope effects are determined with deuterated aniline nucleophiles in the nucleophilic substitution reactions of benzyl benzenesulfonates and 1-phenylethyl benzenesulfonates in acetonitrile at 30.0^{\circ}C. The $k_H/k_D$ values support our previous conclusions regarding the transition state structures proposed for the two reactions based on the cross-interaction constants ${\rho}_{ij}$; the former is a typical $S_N2$ reaction whereas in the latter the four-center transition state may be involved.

• Bulletin of the Korean Chemical Society
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• v.17 no.3
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• pp.254-257
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• 1996

Nucleophilic substitution reactions of 1- and 2-naphthylethyl arenesulfonates, 2 and 3, with anilines and benzylamines in methanol at 65.0 ℃ are investigated. The rates are slower than those for the corresponding derivatives of 2-phenylethyl arenesulfonates, 1, which can be attributed to a greater degree of positive charge stabilization at Cα in the transition state (TS) by a greater electron supply from a phenyl ring compared to a naphthyl ring. The mechanism for the two naphthylethyl systems are similar to that for the 2-phenylethyl derivatives, except that the transition state is formed at somewhat an earlier position along the reaction coordinate. The secondary kinetic isotope effects involving deuterated nucleophilies indicate that naphthylethyl series are sterically more crowded in the TS than 2-phenylethyl system. The data in this work can not elucidate the possible participation of the aryl-assisted pathway in the reaction.

• Bulletin of the Korean Chemical Society
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• v.6 no.3
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• pp.162-164
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• 1985

Nucleophilic substitution reaction of dansyl chloride with anilines in various solvents have been investigated. The Bronsted ${\beta}$ and Hammett ${\rho}_N$ values indicated that the bond formation is advanced more than the bond breaking at the transition state. Solvatochromic correlations also predicted the importance of bond formation at the TS, showing a greater contribution of polarity (${\pi}^{\ast}$) compared to hydrogen bond donor acidity (${\alpha}$). The effect of solvent on rate was found to violate the reactivity-selectivity principle.

• Journal of Electrochemical Science and Technology
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• v.5 no.3
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• pp.87-93
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• 2014

The fluorine-substituted $0.3Li_2MnO_3{\cdot}0.7Li[Mn_{0.60}Ni_{0.25}Co_{0.15}]O_{2-x}F_x$ cathode materials were synthesized by using the transition metal precursor, $LiOH{\cdot}H_2O$ and LiF. This was to facilitate the movement of lithium ions by forming more compact SEI layer and to reduce the dissolution of transition metals. The $0.3Li_2MnO_3{\cdot}0.7Li[Mn_{0.60}Ni_{0.25}Co_{0.15}]O_{2-x}F_x$ cathode material was sphere-shaped and each secondary particle had $10{\sim}15{\mu}m$ in size. The fluorine-substituted cathodes initially delivered low discharge capacity, but it gradually increased until 50th charge-discharge cycles. These results indicated that fluorine substitution gave positive effects on the structural stabilization and resistance reduction in materials.

• Bulletin of the Korean Chemical Society
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• v.18 no.7
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• pp.743-749
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• 1997

Local structure refinement of the BaFe1-xSnxO3-y system (x=0.00-0.50) has been carried out with Fe K-edge x-ray absorpion spectroscopic studies. It is found out that the Fe ions are placed in two different symmetric sites such as tetrahedral and octahedral sites in the compounds by comparison with Fe K-edge x-ray absorption near edge structure (XANES) spectrum of the γ-Fe2O3 compound as a reference. Small absorption peaks of dipole-forbiden transitions appear at a pre-edge region of 7111 eV due to the existence of Fe ions in the tetrahedral and octahedral sites. The peak intensity decreases with the substitution amount of Sn ion. Three different absorption peaks of 1s→4p dipole-allowed transition appear on the energy region between 7123 and 7131 eV. The peaks correspond to 1s→4p main transition of Fe ions in tetrahedral and octahedral sites and 1s→4p transition followed by the shakedown process of ligand to metal charge transfer. The bond distances between Fe ions in the tetrahedral site and nearest neighboring oxygen atom (Fe-4O), and those in octahedral site (Fe-6O) are determined with the extended x-ray absorption fine structure (EXAFS) analysis. Two different interatomic distances increase with the substitution amount of Sn ion and also the bond lengths of Fe-4O are shorter than those of Fe-6O in all compounds.

• Progress in Superconductivity
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• v.13 no.1
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• pp.12-17
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• 2011

We investigated the effects of Ba and Cu co-substitution on the structural and superconducting properties of ($Ru_{1-y}Cu_y$)($Sr_{1.67-x}Ba_xEu_{0.33}$)($Eu_{1.34}Ce_{0.66}$)$Cu_2O_z$ samples. X-ray diffraction(XRD) reveals that single-phase samples can be obtained in the range from x = 0.1 to 0.2 for ($Ru_{0.5}Cu_{0.5}$)($Sr_{1.67-x}Ba_xEu_{0.33}$)($Eu_{1.34}Ce_{0.66}$)$Cu_2O_z$ and from y = 0.25 to 0.5 for ($Ru_{1-y}Cu_y$)($Sr_{1.47}Ba_{0.2}Eu_{0.33}$)($Eu_{1.34}Ce_{0.66}$)$Cu_2O_z$, respectively. All samples with compositions of ($Ru_{0.5}Cu_{0.5}$)($Sr_{1.67-x}Ba_xEu_{0.33}$) ($Eu_{1.34}Ce_{0.66}$)$Cu_2O_z$ (x = 0 - 0.33) show superconducting transition behavior and the onset transition temperature decreases slightly with increasing x in consistent with the change of hole concentration estimated from room temperature thermoelectric power measurements. The XRD and resistivity measurements for the ($Ru_{1-y}Cu_y$)($Sr_{1.47}Ba_{0.2}Eu_{0.33}$)($Eu_{1.34}Ce_{0.66}$) $Cu_2O_z$ system indicate that the partial substitution of Cu for Ru is necessary to form phase pure samples, but result in a small change in transition temperature in the single-phase region from x = 0.25 to 0.5.

• Journal of Magnetics
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• v.18 no.4
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• pp.405-411
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• 2013

The structural, magnetic and magnetocaloric properties of $CoMn_{1-x}Cr_xGe$ (x=0.05-0.125) have been investigated by using electron microscopy, x-ray diffraction, calorimetric and magnetic measurements. In this study, our aim is to justify the magnetocaloric effect by tuning the structural and magnetic transition temperature with Cr doping on CoMnGe pure system. The substitution of Cr for Mn leads to a decrease of both structural and magnetic transition temperatures. However, structural and magnetic transition temperatures do not close to each other. From magnetization measurement, we calculate that isothermal entropy change associated with magnetic transition can be as high as 3.82 J $kg^{-1}K^{-1}$ at 302 K in a field of 7 T. Meanwhile, structural phase transition contribution to isothermal entropy change is calculated as 5.85 J $kg^{-1}K^{-1}$ at 322 K for 7 T.