• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3607-3617
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• 2012

In this paper, the study of various ortho- and meta-substituted Magnolol derivatives is presented. The reaction enthalpies related to three antioxidant action mechanisms HAT, SET-PT and SPLET for substituted Magnolols have been calculated using DFT/B3LYP method in gas-phase and water. Calculated results show that electron-withdrawing substituents increase the bond dissociation enthalpy (BDE), ionization potential (IP) and oxidation/reduction enthalpy (O/RE), while electron-donating ones cause a rise in the proton dissociation enthalpy (PDE) and proton affinity (PA). In ortho- position, substituents show larger effect on reaction enthalpies than in meta-position. In comparison to gas-phase, water attenuates the substituent effect on all reaction enthalpies. In gas-phase, BDEs are lower than PAs and IPs, i.e. HAT represents the thermodynamically preferred pathway. On the other hand, SPLET mechanism represents the thermodynamically favored process in water. Results show that calculated enthalpies can be successfully correlated with Hammett constants (${\sigma}_m$) of the substituted Magnolols. Furthermore, calculated IP and PA values for substituted Magnolols show linear dependence on the energy of the highest occupied molecular orbital ($E_{HOMO}$).

• Journal of the Korean Chemical Society
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• v.53 no.2
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• pp.159-165
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• 2009

The synthesis of 2-amino-5-substituted-1,3,4-oxadiazoles 4 were carried out from the electrooxidation of semicarbazone 3 at the platinum electrode under controlled potential electrolysis in an undivided cell. This is an environmentally benign method in the field of synthetic organic chemistry. The non-aqueous solvents acetic acid and acetonitrile and a supporting electrolyte lithium perchlorate were used for the electrolysis in the electrooxidation. The products were structurally charecterised by IR, $^1H$-NMR, $^{13}C$-NMR and elemental analysis.

• Journal of the Korean Chemical Society
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• v.53 no.3
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• pp.340-344
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• 2009

HEMA/vinyl-substituted polyphosphazene was prepared by the ring-opening polymerization of phosphonitrillic chroride trimer at $200{\sim}300\;{^{\circ}C}$, followed by Grignard reaction with vinyl magnesium bromide and then by the reaction with HEMA(2-hydroxyethyl methacrylate). HEMA/vinyl-substituted polyphosphazene was copolymerized with EGDMA(ethylene glycol dimethacrylate; used as a cross-linker for the free-radical copolymerization), NVP (N-vinyl-pyrrolidone) in the presence of AIBN (azobisisobutyronitrile) as a radical initiator. The oxygen transmissibility, water content and visible-ray transmissibility of the resulting copolymer were measured to be Dk/t 88, 30.89% and 87%, respectively, indicating that the copolymer can be used as a good contact lens material.

• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2335-2339
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• 2013

Relative reactivity of various Al-substituted dialkylalans ($AlR_2(X)$) in reduction of acetone has been studied with density functional theory and MP2 method. Formation of the alan dimers and the alan-acetone adduct, and the transition state for the Meerwein-Ponndorf-Verley (MPV) type reduction of the adduct were calculated to figure out the energy profile. Formation of dimeric alans is highly exothermic. Both the relative free energies for acetone-alan adduct formation and the TS barriers for the MPV type reduction with respect to alan dimers and acetone were calculated and they show the same trend. Based on these energetic data, relative reactivity of alans is expected to be; $AlR_2(Cl)$ > $AlR_2(OTf)$ > $AlR_2(O_2CCF_3)$ > $AlR_2(F)$ > $AlR_2(OMs)$ > $AlR_2(OAc)$ > $AlR_2(OMe)$ > $AlR_2(NMe_2)$. The energy profile is relatively well correlated with the experimental order of the reactivity of Al-substituted dialkylalans. It is noted that the substituents of alans have initial effects on the relative free energies for the carbonyl-adduct formation. Therefore, an $AlR_2(X)$ which forms a more stable carbonyl-adduct is more reactive in carbonyl reduction.

• Korean Journal of Crystallography
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• v.7 no.2
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• pp.165-174
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• 1996

The effects of Ba2+, Sr2+, and Ca2+-substitutions for Pb2+ at Pb(Zr0.52Ti0.48)O3 composition were studied for thier dielictric, piezoelectric, and aging properties. For relative dielectric constants and electromechanical coupling factors, the Ba2+-substituted composition was the highest and the Ca2+-substityed composition was the lowest. In the case of mechanical quality factors, the opposite behavior occurred. Time dependence of frequency for various ion-substituted compositions is similar to that of non-substituted composition. The piezoelectric properties after aging at high temperature was the worse than that after aging at room temperature.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.4
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• pp.543-550
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• 2017

Various chemical properties including density and heat of formation of 1-substitued trinitroimidazoles (TNIs) were estimated by using density functional theory (DFT). Using chemical properties estimated by DFT, explosive performance and sensitivity of 1-substitued TNIs were analyzed by following the ADD Method-1 procedure. The results were displayed on two-dimensional performance-sensitivity plot, and were compared with those of explosive molecules commonly used in many military systems. Different 1-substituents of TNI made that both explosive performance and impact sensitivity were changed significantly. Methyl substituted TNI became moderately insensitive and slightly less powerful. Amino, fluoro, picryl, and difluoroamino substituted TNIs were highly powerful like RDX and HMX, but greatly sensitive. Nitro substituted TNI was predicted to be extremely sensitive to be handled as a secondary explosive.

• Bulletin of the Korean Chemical Society
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• v.13 no.4
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• pp.425-428
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• 1992

Sodium substituted samples of $Y_{1-x}Na_xBa_2Cu_3O_{7-y}$ for $0.00{\leq}x{\leq}0.16$ were prepared and characterized by X-ray powder pattern, electrical resistivity and magnetic susceptibility measurements, Raman spectroscopy, and idometric titration. The Na substituted compounds have narrow solid solution limits where $0.00{\leq}x{\leq}0.16.$ As the Na concentration increases, the parent orthorhombic structure tends to gradually change to tetragonal. Small changes in the superconducting transition temperature, Tc, are observed in this solid solution region. Raman spectra for the Na phases are virtually identical with that of $YBa_2Cu_3O_7$ except that the Cu(1)-O(4) stretching mode at 504 $cm^{-1}$ and the Cu(2)-O(2,3) bending mode at 340 $cm^{-1}$ for x = 0.16 are slightly shifted. The hole concentrations of the sodium substituted compounds ranged from 0.31 to 0.33 per Cu site are increased with Na content. The substitution of $Na^+$ for $Y^{3+}$ site appears to create oxygen vacancies in the Cu-O chains, causes structural change from orthorhombic to tetragonal, and increases hole concentration in the substituted system.

• Bulletin of the Korean Chemical Society
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• v.14 no.5
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• pp.546-548
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• 1993

The discrete structure of substituted 9-benzonorbornenyl cation 3a and 3c was studied using the empirical ${\Delta}$J equation which was developed by Kelly and coworker$^5$. The ${\Delta}$J values of substituted 9-benzonorbornenyl cations were obtained from p-methyl-6,7-dimethyl benzonorbornen-9-yl (3a) and 9-methyl-6,7-dimethyl benzonorbonen-9-yl (3c) cations under stable ion conditions, and were compared with those of the corresponding ketone analog; these cations were generated by dissolving the corresponding carbinols in superacid at -120$^{\circ}$C and the nmr spectra taken at -60$^{\circ}$C~-90$^{\circ}$C. The ${\Delta}$J values are 8.7 Hz for the bridgehead carbons in cation 3c and 3.1 Hz for cation 3b. The ${\Delta}$J values at C5,8 in fused benzene ring are 14.3 Hz for cation 3c and 8.7 Hz for cation 3a. The excellent correlation of the ${\Delta}$J values with 1$^9F$ chemical shifts of p-fluorophenyl-6,7-dimethylbenzonorbornenyl cation (3d) indicate that ${\Delta}$J value is a reliable probe to charge density at adjacent cationic carbon. These NMR parameters strongly support that the symmetrically ${\pi}$-bridged nonclassical structure (type 2) of substituted 9-benzonorbornenyl cations in stable ion conditions.

• Bulletin of the Korean Chemical Society
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• v.18 no.6
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• pp.644-648
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• 1997

Introduction of an alkyl substituent at the $C_{4\beta}$ position of antimalarial trioxanes has caused them to become more active in their antimalarial activity. We have designed a structurally simple 4β-phenyl substituted trioxane (3) as an active antimalarial since it can form a more stable carbon radical when reacting with ferrous bromide. The trioxane 3 has been prepared along with the corresponding isomer 4 according to the previously reported procedure. The synthesized trioxanes 3 and 4 were finally separated by using HPLC and assigned their stereochemistry by spectroscopy and X-ray crystallography. Their antimalarial activities were surprisingly low. The low activity was then rationalized based on the product distribution of the ferrous ion induced reaction of these trioxanes. These trioxanes with ferrous bromide did not produce any detectable amount of the corresponding $C_4$-hydroxylated product, consistent with the fact that neither $C_{4\beta}$-phenyl substituted nor $C_{4\alpha}$-phenyl substituted trioxane has any antimalarial activity. It implies that a $C_4$ substituent of antimalarial trioxanes has to stabilize an adjacent carbon-centered radical in a specific stability range in order to show a good antimalarial activity. This study, combined with related studies, could help develop more potent antimalarial trioxanes.

• Bulletin of the Korean Chemical Society
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• v.33 no.5
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• pp.1457-1464
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• 2012

An ecofriendly catalytic route for selective synthesis of $N$-substituted azacyclopentanes, nitrogen-containing heterocyclic intermediates for many bioactive compounds, was established by carrying out $N$-heterocyclization (di $N$-alkylation) of primary amines with 1,4-dichloro butane (as dialkylating agent) using catalytic amount of hydrotalcite as solid base catalyst. The hydrotalcite was found to be efficient solid base catalyst for di $N$-alkylation of different primary amines (aniline, benzyl amine, cyclohexyl amine and n-butyl amine) giving 82 to 96% conversion (at optimized reaction condition) of 1,4-dichloro butane and > 99% selectivity of respective $N$-substituted azacyclopentanes within 30 min. under solvent free condition. The reaction parameters significantly influence the conversion of 1,4-dichloro butane to $N$-substituted azacyclopentanes. The nature of substituent present on amino group affects the reactivity of amine substrates for di $N$-alkylation reaction with 1,4-dichloro butane. The 1,4-dichloro butane was found to be highly reactive alkylating agent for di $N$-alkylation of amines as compared to 1,4-dihydroxy butane. The reusability of the catalyst and its chemical stability in the reaction was demonstrated.