• Bulletin of the Korean Chemical Society
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• 제15권6호
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• pp.453-455
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• 1994

Semiempirical MO calculations are applied to estimate the substituent effects on acylations of the nonfused N-vinyl-2-amino $\beta-lactams$ having frameworks analogous to 3-cephems. The stabilization energy for the reaction intermediate of the nucleophilic attack by the hydroxide ion is selected as the reactivity index and calculated by AM1 and PM3 methods for the model $\beta-lactams$ with substituents at the C1 and N-vinyl terminal positions. The reactivities are larger for -SH connected to the C1 and strong $\pi-acceptors$ at the N-vinyl terminal implying the large reactivity for known active cephalosporins. Quantum chemical calculation of stabilization energy could be useful in correlating antibiotic activities of many compounds obtained as derivatives of a lead compound.

• Bulletin of the Korean Chemical Society
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• 제20권10호
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• pp.1172-1176
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• 1999

Nucleophilic substitution reaction of Y-benzyl bromide with X-pyridines are investigated in DMSO at 45.0℃. Biphasic rate dependence is observed on varying the substituents in the substrate (Y) as well as in the nucleophile (X). The two well-defined straight lines in the Hammett (ρy) and Bronsted ( βx) plots are interpreted to indicate the changes in transition-state structure, a decrease in bond cleavage as the substituent on the substrate is changed from electron-donors ( ρy < 0) to electron-acceptors ( ρy > 0), and an increase in the extent of bond formation with the corresponding changes of the substituent on the pyridine. A Jencks' type analysis of separate polar (ρ) and resonance (ρr) effects can also be accounted for by the change of the transition-state structure, not by the variable combination of polar and resonance effects.

• Bulletin of the Korean Chemical Society
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• 제16권7호
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• pp.604-609
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• 1995

The relative dissociation constants of 4-substituted bicyclo[2,2,2]octane-1-carboxylic acids, 4-substituted quinuclidines, and 3-and 4-substituted pyridines were collected from a number of sources. In order to understand the actual substituent effects with a combination of inductive effect (σI) and resonance effect (σR) components. The DSP correlation has been employed statistically for each of the p-and m-series. The inductive effect from the m-position was 1.2 times more effective than that from the p-position and the requirement of σR+ for the best-fit led to the conclusion that pyridine system belongs to the σ+-class reactivity. Also compared with results from Yukawa-Tsuno's LArSR treatment and relevant treatment.

• Bulletin of the Korean Chemical Society
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• 제7권3호
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• pp.186-190
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• 1986

Effects of substituents in the nucleophile(X), the substrate(Y) and the leaving group(Z) on the structure of $S_N2$ transition states have been analyzed by considering effects of four components, electrostatic($E_{es}$), exchange repulsion ($E_{ex}$), polarization($E)_{pl}$) and charge transfer($E_{ct}$) terms, of interaction between the reactants on the degree of bond making and bond breaking. Prediction of net effects of all substituents(X, Y and Z) on the degree of bond making were found to be clearcut whereas the effect of an electron withdrawing group on the substrate (Y = EWG) on the degree of bond breaking was complex; the substituent(Y = EWG) is normally carbon-leaving group($C^{\ast}$-L) bond tightening($E_{pl}$ dominance) but becomes $C^{\ast}$-L bond loosening when the bond is strongly antibonding ($E_{ct}$ dominance). Our model calculations on the reaction of $CH_2XNH_2$ with $YCH_2COOCH_2Z$ using energy decomposition scheme have confirmed that predictions based on our analysis are correct.

• Bulletin of the Korean Chemical Society
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• 제16권3호
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• pp.277-281
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• 1995

The relationship between the signs of ${\rho}i(0)$, ${\rho}j(0)$ and ${\rho}ij$ and validity of the reactivity-selectivity principle (RSP) has been derived: RSP is valid when W = ${\rho}i(0){\cdot}{\rho}j(0)/{\rho}ij$ is negative. The analysis of 100 reaction series indicated that for normal SN2 reactions involving variations of substituents in the nucleophile (X) and in the substrate (Y) RSP is valid only for a dissociative type for which ${\rho}Y(0)$ is negative, whereas for the acyl transfer reactions with rate-limiting breakdown of the tetrahedral intermediate RSP is valid in general for all substituent changes, X, Y and/or Z (substituent on the leaving group). The trends in the validity of RSP for certain types of reaction can be useful in supplementing the mechanistic criteria based on the signs of ${\rho}i(0)$, ${\rho}j(0)$ and ${\rho}ij$.

• Bulletin of the Korean Chemical Society
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• 제12권3호
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• pp.295-301
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• 1991

The nucleophilic substitution reactions of p-substituted benzenesulfonyl chlorides wiht p-substituted anilines were carried out in 1,1,1,3,3,3-hexafluoro-2-propanol and 2-propanol mixtures. The salt effect was observed to be inhibited by the reaction of 1,1,1,3,3,3-hexafluoro-2-propanol with nucleophiles. To investigate the effectiveness of the salt for the nucleophilic substitution reaction the relative salt effect was determined. According to the comparison with the inhibitive salt effect and the substituent effects for the substrates and nucleophiles, the reactions were predicted to be controlled by the salt effect more than substituent effect in HFP-PrOH mixtures.

• 한국염색가공학회지
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• 제33권4호
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• pp.169-181
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• 2021

Five dyes based on phthalocyanine, a dye on azo, and a dye on anhraquinone were prepared from corresponding starting material to investigate the effects of substituent on thermal-stability of dyes which is essentially required to apply to the color filters. Synthesized dyes were confirmed their chemical structure using by 1H-NMR, MASS and Elemental analysis. The thermal-stability was evaluated by the weight reductions measured by TGA analysis comparing to that of conventional C.I. Pigment Blue 15:6. The absorption maxima were measured by UV-VIS spectrophotometer then the effects of substituent on absorption maximum was also investigated.

• Bulletin of the Korean Chemical Society
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• 제23권5호
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• pp.758-760
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• 2002

• 한국광과학회:학술대회논문집
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• 한국광과학회 1999년도 학술대회지
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• pp.83-83
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• 1999

• 대한화학회지
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• 제42권4호
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• pp.10-467
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• 1998