• Title/Summary/Keyword: substituent effect

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Relation of Structural Features of Dinuclear Constrained Geometry Catalysts with Copolymerization Properties of Ethylene and 1-Hexene (이핵 CGC의 구조적인 특성과 에틸렌/1-헥센의 공중합 거동과의 관계)

  • Cao, Phan Thuy My;Nguyen, Thi Le Nhon;Nguyen, Thi Le Thanh;Noh, Seok-Kyun
    • Polymer(Korea)
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    • v.35 no.6
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    • pp.505-512
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    • 2011
  • Effects of structural features of 4 dinuclear constrained geometry catalysts having paraxylene derivative bridge (DCGC) on copolymerization of ethylene and 1-hexene were investigated. The bridges of three catalysts have para-xylene backbone with a different substituent at benzene ring. The substituents were hydrogen (Catalyst 1), isopropyl (Catalyst 2), n-hexyl (Catalyst 3) and 1-octyl (Catalyst 4). It was found that Catalyst 1 having hydrogen as a substituent exhibited the greatest activity among the four dinuclear CGCs. On the other hand, Catalyst 2 containing isopropyl as a substituent showed the smallest activity. Very interestingly, Catalyst 2 was able to produce about 6 times higher molecular weight polymer than Catalyst 3 and 4. Catalyst 3 and 4 having a long alkyl chain substituent revealed the biggest comonomer response to generate polyethylene copolymer containing more than 40% 1-hexene contents. These results suggest that the control of the substituent of para-xylene bridge of dinuclear CGC can provide a proper method to adjust the microstructure of polyethylene copolymers.

Kinetic and Theoretical Studies on Pyridinolysis of 2,4-Dinitrophenyl X-Substituted Benzoates: Effect of Substituent X on Reactivity and Mechanism

  • Um, Ik-Hwan;Kim, Eun-Hee;Im, Li-Ra;Mishima, Masaaki
    • Bulletin of the Korean Chemical Society
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    • v.31 no.9
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    • pp.2593-2597
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    • 2010
  • Second-order rate constants ($k_N$) have been measured spectrophotometrically for reactions of 2,4-dinitrophenyl X-substituted benzoates (X = 4-MeO, H and 4-$NO_2$) with a series of Z-substituted pyridines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plots exhibit downward curvature (e.g., $\beta_2$ = 0.89 ~ 0.96 when $pK_a$ < 9.5 while $\beta_1$ = 0.38 ~ 0.46 when $pK_a$ > 9.5), indicating that the reaction proceeds through a stepwise mechanism with a change in rate-determining step (RDS). The ${pK_a}^o$, defined as the $pK_a$ at the center of Br${\o}$nsted curvature, has been analyzed to be 9.5 regardless of the electronic nature of the substituent X in the benzoyl moiety. Dissection of $k_N$ into the microscopic rate constants $k_1$ and $k_2/k_{-1}$ ratio has revealed that $k_1$ is governed by the electronic nature of the substituent X but the $k_2/k_{-1}$ ratio is not. Theoretical calculations also support the argument that the electronic nature of the substituent X in the benzoyl moiety does not influence the $k_2/k_{-1}$ ratio.

Theoretical Studies on the Progonation Equilibria of Benzoyl Derivatives

  • Kim, Wang Gi;Kim, Yong Bin;Kim, Chang Gon;Lee, Bon Su
    • Bulletin of the Korean Chemical Society
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    • v.22 no.4
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    • pp.395-400
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    • 2001
  • The effects of ortho- (R = H and CH3) and Y-substituents (Y = OCH3, CH3H and CN), which are directly attached to the carbonyl carbon, on the protonation equilibria of the para-X-substituted benzoyl derivatives, 4-X -2, 6-di-R-C6H2-C(=O)-Y, are investigated theoretically using the B3LYP method with 6-31+G* basis set. Structurally, both of the (B) and (BH+ ) forms in the species with R = H are nearly coplanar regardless of the Y-substituents implying that the steric repulsion between Y-substituent and R = H is relatively small. In the species with R = CH3 , the tortional angle (Θ) between the carbonyl moiety and aryl ring varies from zero to near right angle depending on the degree of steric repulsion between Y and R = CH3 and the resonance demand. However the reaction energies, ΔG°, for the protonation processes are more favorable for R = CH3 than for R = H due to stronger electron donating effect of R = CH3 , although the species with R = CH3 are unfavorable sterically. On the other hand, the Hammett type plots are progressively better correlated with б+ than with б values on going from Y = OCH3 to Y = CN for both species with R = H and CH3 indicating that the degree of resonance delocalization between carbonyl moiety and X-substituent is increased for a more electron accepting Y-substituent. Nevertheless the effects of R = CH3 on the magnitude of Hammett type reaction constants ( б or б+ ) are not much different from those of R = H.

Clinnamic Acid Derivatives II, The Kinetics and Mechanism of the Hydrolysis of Benzalacetophenone Derivatives (신남산 유도체 II, Benzalacetophenone 유도체의 가수분해 메카니즘과 반응속도론적 연구)

  • Hwang, Yong-Hyun;Lee, Ki-Chang;Ryu, Jung-Wook;Lee, Kwang-Il;Choi, Bong-Jong
    • Journal of the Korean Applied Science and Technology
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    • v.6 no.2
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    • pp.67-74
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    • 1989
  • The Kinetics of the Hydrolysis of benzalacetophenone derivatives has been investigated by ultraviolet spectrophotometry in 5% dioxane - $H_2O$ at $50^{\circ}C$. A rate equation which can be applied over wide pH range was obtained. The substituent effect on the hydrolysis of benzalacetophenone derivatives were facilitated by electron attracting groups. Based on the rate equation, substituent effect, general base effect, activation parameters and final product, the hydrolysis of benzalacetophenone derivatives seems to be initiated by the netural molecule of $H_2O$ which does not dissociate at below pH 9.0 but proceeded by the hydroxide ion at above pH 11.0. In the range of pH $9.0{\sim}11.0$ these two reactions occur competitively.

Spectroscopic Studies on Interaction of Protoberberines with the Deoxyoligonucleotide d(GCCGTCGTTTTACA)2

  • Park, Hye-Seo;Kim, Eun-Hee;Kang, Mi-Ran;Chung, In-Kwon;Cheong, Chae-Joon;Lee, Weon-Tae
    • Bulletin of the Korean Chemical Society
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    • v.25 no.10
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    • pp.1559-1563
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    • 2004
  • The topoisomerase II poisoning effect of certain protoberberine alkaloids is associated with anti-cancer activity. Structure-activity relationships of protoberberine analogues substituted on the ring protons reveal that substitution at the C19 position is an important determinant of biological activity. In this study, the effects of substituent modification at the C19 position on the interaction of protoberberines with DNA are determined using UV and NMR spectroscopy. The line broadening effect on aliphatic resonances, chemical shift changes of the imino protons of HP14 upon berberine and berberrubine binding to HP14, and the rate of the exchange process between protoberberine analogs bound indicate that berberrubine binds HP14 more specifically than berberine. In addition, the free HP14 is altered by the substituent at the 19-position. UV spectra of berberrubine have shown a hypochromic effect together with a slight red shift, which are usually regarded as characteristics of DNA intercalation. These results are consistent with our previous report that the berberrubine is partially intercalated with HP14 with molar ratio 1 : 1, whereas a non-specific interaction is predominant between the berberine and HP14.

Tailoring the Excited-State Intramolecular Proton Transfer (ESIPT) Fluorescence of 2-(2'-Hydroxyphenyl)benzoxazole Derivatives

  • Seo, Jang-Won;Kim, Se-Hoon;Park, Sang-Hyuk;Park, Soo-Young
    • Bulletin of the Korean Chemical Society
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    • v.26 no.11
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    • pp.1706-1710
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    • 2005
  • The excited-state intramolecular proton transfer (ESIPT) fluorescence in the 2-(2'-hydroxyphenyl)benzoxazole (HBO) derivatives with different electron donor and acceptor substituents was studied by spectroscopic and theoretical methods. Changes in the electronic transition, energy levels, and orbital diagrams of HBO analogues were investigated by the semi-empirical molecular orbital calculation and were correlated with the experimental spectral position of ESIPT keto emission. It was found that the presence of substituents, regardless of their nature, resulted in the red-shifted absorption relative to HBO. However, the spectral change of the ESIPT fluorescence was differently affected by the nature of substituent: hypsochromic shift with electron donor and bathochromic shift with electron acceptor.

SUBSTITUENT EFFECT ON THE INHIBITION OF CHLOROPHYLL FORMATION BY N-PHENYL OXADIAZOLIDINEDIONE DERIVATIVES IN CUCUMBER AND SPECULATION ON THE HERBICIDAL ACTION

  • Hwang, Kwang-Jin;Kim, Hyung-Jin;Kim, Jin-Seog
    • Journal of Photoscience
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    • v.3 no.3
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    • pp.137-140
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    • 1996
  • The inhibition of chlorophyll formation in cucumber cotyledons by N-phenyl oxadiazolidinedione derivatives Ia-u showed similar trend as their herbicidal activities. In case of oxadiazolidinedione Iq, with a propargyloxy substituent, both the highest herbicidal activity and inhibitory action(pI$_{50}$ = 6.37) were observed. The accumulation of protoporphyrin IX and cellular electrolyte leakage by oxadiazolidinedione Ia, Ik and Iq were well correlated with their inhibition of chlorophyll biosynthesis. These results suggest that the herbicidal activity of oxadiazolidine Ia-u is originated from the inhibition of chlorophyll biosynthesis.

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Substituent Effects on the Binding Energies of Benzyl Alcohol-H2O Clusters: Ab initio Study

  • Ahn, Doo-Sik;Lee, Sung-Yul
    • Bulletin of the Korean Chemical Society
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    • v.23 no.2
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    • pp.262-266
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    • 2002
  • Computations are presented for the ortho- and para-substituted benzyl alcohol-$H_2O$ clusters. A variety of conformers are predicted, and their relative energies are compared. Binding energies of the clusters are computed, and detailed analysis is presented on the effects of substitution on the strength of the hydrogen bond in the clusters. F- and $NH_2-$ substituted clusters are studied to analyze the effects of electron-withdrawing and electron-pushing groups. In para-substituted clusters, the inductive effects are dominant, affecting the binding energies in opposite way depending on whether the hydroxyl group is proton-donating or -accepting. For ortho-substituted clusters, more direct involvement of the substituting group and the resulting geometry change of the hydrogen bond should be invoked to elucidate complicated pattern of the binding energy of the clusters.

Investigation of the Annealing Time Effects on the Properties of Sputtered ZnO:Al Thin Films

  • Kim, Deok Kyu;Kim, Hong Bae
    • Applied Science and Convergence Technology
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    • v.23 no.6
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    • pp.366-370
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    • 2014
  • ZnO:Al transparent conductive films were deposited on glass substrates by RF magnetron sputtering technique and annealed by rapid thermal annealing system. The influence of annealing time on the structural, electrical, and optical properties of ZnO:Al thin films was investigated by atomic force microscopy, X-ray diffraction, Hall method and optical transmission spectroscopy. As the annealing time increases from 0 to 5 min, the crystallinity is improved, the root main square surface roughness is decreased and the sheet resistance is decreased. The lowest sheet resistance of ZnO:Al thin film is 90 ohm/sq. The reduction of sheet resistance is caused by increasing carrier concentration due to substituent Al ion. All films are transparent up to 80% in the visible wavelength range and the adsorption edge is a blue-shift due to Burstein-Moss effect with increasing annealing time.

Selective Reduction of Organic Compounds with Al-Trifluoromethanesulfonyldiisobutylalane. Comparison of Its Reactivity with Al-Methanesulfonyldiisobutylalane

  • Cha, Jin-Soon
    • Bulletin of the Korean Chemical Society
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    • v.32 no.1
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    • pp.219-224
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    • 2011
  • The new MPV type reagent, Al-trifluoromethanesulfonyldiisobutylalane ($DIBAO_3SCF_3$), has been prepared and its reducing characteristics in the reduction of selected organic compounds containing representative functional groups have been examined, and compared its reactivity with that of Al-methanesulfonyldiisobutylalane ($DIBAO_3SCH_3$) in order to understand the fluorine-substituent effect on its reactivity. In general, the reactivity of $DIBAO_3SCF_3$ appears to be much higher than that of $DIBAO_3SCH_3$, apparently due to the acidity increase by the electron-withdrawing fluorine-substituent. The reagent reduced aldehydes and ketones readily, but showed a perfect selectivity in the reduction of $\alpha,\beta$-unsaturated aldehydes and ketones to produce the corresponding allylic alcohols in an absolutely 100% purity. In addition, the reagent achieved the regioselective cleavage of phenyl- or/and alkyl-substituted epoxides to the less substituted alcohols in a perfect regioselectivity. Moreover, the reagent also showed an high stereoselectivity in the reduction of substituted cycloalkanones to produce the thermodynamically more stable alcohol epimers exclusively.