• Journal of the Korean Chemical Society
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• v.32 no.3
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• pp.243-248
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• 1988

The hypersensitive $f{\rightarrow}f$ transitions of Nd(III), Ho(III), and Er(III) have been studied for some lanthanide complexes in aqueous solution. Based on the linear correlation between the oscillator strength of the transition and the basicity$(pK_a)$ of the ligand, the covalency in the metal-ligand bonding is discussed for lanthanide anthranilate, pyrazine-2-carboxylate, and pyruvate.

• Journal of Welding and Joining
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• v.2 no.2
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• pp.1-6
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• 1984

피복아아크 용접봉(이하 용접봉이라 함)의 피복제는 염기도에 따라 산성, 중성, 염기성으로 대별할 수 있다. 용접에서의 화학야금반응은 제강의 화학야금반응과 원리는 비슷하나 양자간 크게 다른 점은 용접시의 반응시간이 극히 짧다는 점이다. 이와같이 반응시간이 짧다는 점 이외에도 작업자가 직접 용융반응을 지켜 보면서 반응후에 나타나는 제반 문제점에 대비하여야 하는 어려운 점이 있다. 제강반응은 전문가만의 독특한 기술인 반면 용접은 용접봉 제조자 뿐만 아니라, 용접작업자 고유의 기술이므로 용접야금반응을 상식화 하고자 하는데 본 고는 의의를 두고 있다. 피복제 중에서의 염기도의 변화, 즉 염기도에 영향을 크게 미치는 탄산칼슘의 양을 임의로 변화시키므로서 다음과 같은 현상을 기대할 수 있다. (1)용접 작업성의 변화 (2)용착 금속의 화학성분 변화 (3)용착금속의 조직 변화 (4) 용착금속내의 수소 함유량 변화 (5)용착금속의 기계적 성질변화 등이다.

• Bulletin of the Korean Chemical Society
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• v.18 no.1
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• pp.86-91
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• 1997

Complexation of primary alkylammonium ions by 1, 3-distal calix[4]arene diesters was studied by NMR spectroscopy. The guest alkylammonium ions are found to bind mainly to the two ester moieties and are oriented outward with respect to the cone cavity of the host, forming exo-type complexes unlike the case of alkylammonium-calix[6]arene systems. Measurement of T1 also revealed that the primary binding site is the two ester moities and phenolic OH groups. The temperature dependence of the chemical shifts of phenolic OH protons in these diesters correlates with the basicity of the solvent moderately well and the temperature coefficients of their chemical shifts are found to significantly decrease upon complexation with propylammonium ion.

• Bulletin of the Korean Chemical Society
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• v.19 no.1
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• pp.110-114
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• 1998

The hydrogen-bonding interactions between thioacetamide (TA) and urea derivatives such as tetramethylurea (TMU) and dimethyldiphenylurea (DMDPU) have been studied using near-infrared absorption spectroscopy. Thermodynamic parameters for the interactions between TA and urea derivatives were determined by analyzing the $v^{as}_{N-H}$+Amide Ⅱ combination band of TA at 1970 nm. The ΔH° values, indicating the intrinsic strength of hydrogen bonding, are - 23.0 kJ/mole and - 19.8 kJ/mol for TMU and DMDPU, respectively. This is well explained by the inductive effects of substituents. Ab initio molecular orbital calculations for the proton affinity of TMU, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) in gas phase have been carried out at HF/3-21G ad HF/6-31G(d) levels, showing that the proton affinity of TMU is larger than that of DMA, which agrees well the experimental results.

• Bulletin of the Korean Chemical Society
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• v.13 no.2
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• pp.122-127
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• 1992

Some perovskites $A($Cu_{1}3}Nb_{2}3}$)O_3(A=$Sr^{2+}$$, $Ba^{2+}$ and $Pb^{2+}$) and their series of mixed perovskites have been prepared by solid state reaction. Single perovskite phase was obtained in Sr or Ba rich samples, but pyrochlore phase was found in Pb rich samples. The stability of perovskite phase is dependent on the ionicity of bonding as well as the tolerance factor. All the obtained perovskites have tetragonal symmetry distorted by Jahn-Teller effect of $Cu^{2+}$. In the case of $Sr(Cu_{1}3}Nb_{2}3})O_3$, some superlattice lines caused by threefold enlarging of fundamental unit cell were observed. And, the symmetry of B site octahedron and the bonding character of B-O bond have been studied by IR, ESR and diffuse reflection spectroscopy. It appeared that the symmetry and the bonding character are influenced by such factors as the size and the basicity of A cation.

• Bulletin of the Korean Chemical Society
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• v.18 no.8
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• pp.865-868
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• 1997

Second-order rate constants have been measured spectrophotometrically for the reactions of p-nitrophenyl phenylacetate (1) and benzoate (2) with a series of alicyclic amines in H2O containing 20 mole % DMSO at 25.0 ℃. 1 appears to be more reactive than 2 toward all the amines studied, although phenylacetic acid is a weaker acid than benzoic acid. The higher reactivity of 1 can be attributed to resonance and/or steric effect, since the ground state of 2 can be stabilized by resonance and 1 would experience less steric hindrance due to the presence of CH2 group between phenyl and C=O group. The reactivity of the amines increases with increasing their basicity. The Bronsted-type plots for aminolysis of 1 and 2 show good linearity with βnuc values of 0.81 and 0.85, respectively, indicating that the TS structures of the aminolyses of 1 and 2 are similar. Besides, the linear Bronsted plots obtained in the present system clearly suggest that there is no mechanism change for the given series of the amines and the reactions of 1 and 2 proceed in a same mechanism.

• Bulletin of the Korean Chemical Society
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• v.14 no.4
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• pp.457-461
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• 1993

Bioconcentration factors (BCF) in fish of organic nonelectrolytes are well correlated by a linear solvation energy relationship (LSER) of the form : log BCF= -0.95 + 4.74 $V_I/100 - 4.39{\beta} + 0.88{\alpha}$ where $V_I$ is the intrinsic solute molecular volume and ${\beta}$ and ${\alpha}$ are the solvatochromic parameters that measure hydrogen bond acceptor basicity and donor acidity of the compound. The LSER model can not only correlate the property with an accuracy comparable to molecular connectivity model but also provide a quantitative informationon on the nature and relative strength of solute-target system interactions affecting the property of interest. Such an information can hardly be obtained from molecular connectivity model.

• Bulletin of the Korean Chemical Society
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• v.12 no.5
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• pp.560-564
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• 1991

The gas-phase pyrolysis reactions of iminoethers (Ⅱ), 2-alkoxypyridines (Ⅲ), 2-N-alkylated pyridones (Ⅳ) and N-alkylated acetamides (Ⅴ) have been studied MO theoretically with the AM1 method. The decomposition of these compounds proceeds by a concerted retro-ene process through a six-membered cyclic transition state. The reactivity decreases in the order (Ⅱ) > (Ⅲ) > (Ⅳ) > (Ⅴ), with a greater reactivity for the imine series, (Ⅱ) and (Ⅲ), compared to the amide series, (Ⅳ) and (Ⅴ), and a difference in basicity between the N and O atoms. Within a given series, however, the reactivity is dictated mainly by the aromaticity in the transition state. The reactivity order with respect to side alkyl chain of a species was found to increase as the steric crowding effect increases. The AM1 reactivity in this work agree well with the experimental results.

• Bulletin of the Korean Chemical Society
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• v.14 no.5
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• pp.594-598
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• 1993

The protonation constants of the 14-membered tetraaza macrocycles A(3,14-dimethyl-2,6,13,17-tetraazatricyclo$[l6.4.0^{1,18}.0^{7,12}]$docosane) and B(2,3,6,13,14,17-hexamethyl-2,6,13,17-tetraazatric yclo-[l6.4.$0^{1,18}.0^{7,12}$]docosane) were measured by potentiometry. The formation constants of each of these ligands with copper(II) and nickel(II) were determined by an out-of-cell spectrophotometric method. The results indicate that the per-N-methylated macrocycle B exhibits much higher selectivity for complex formation with copper(II) over nickel(II) ion than A and other related 14-membered tetraaza macrocycles. The effects of the N-and C-substituents on the basicity and the metal ion selectivity of the ligands are discussed. The synthesis and properties of copper(II) and nickel(II) complexes of B are also described.

• Journal of Integrative Natural Science
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• v.5 no.3
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• pp.175-181
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• 2012

Oxepane high explosives substituted to explosive group such as azido, nitrato and hydrazino are investigated theoretically the acid catalyzed reaction using the semiempirical MINDO/3, MNDO and AM1 methods to use as the guidelines of high explosives. The nucleophilicity and basicity of oxepane high explosives can be explained by the value of negative charge on oxygen atom of oxepane and the reactivity in propagation step can be represented by the value of positive charge on carbon atom and low electrophile LUMO energy. It was known that carbenium ion was favorable due to the stable energy (19.507~32.101 Kcal/mol) between oxonium ion and carbenium ion in the process of cyclic oxonium ion of oxepane high explosives being converted to open carbenium ion in oxepane high explosives. The value of concentration of cyclic oxonium ion and open carbenium ion in equilibrium status was found to be a major determinant of mechanism, it was expected to react faster in the prepolymer propagation step in SN1 mechanism than in that of $S_N2$.