• Bulletin of the Korean Chemical Society
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• v.19 no.5
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• pp.527-530
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• 1998

This paper presents the electrochemistry and molecular orbital (MO) picture of a series of conformationally-restricted thioxantone derivatives. A series of $C_2-substituted$ thioxanthones were examined to probe the electronic influence of the substituent on the electrooxidation and electroreduction sites (i.e., on the electron densities at the 10-and 9-positions), respectively. In the presence of "electrophoric" groups such as C=O and S, characteristic electrochemical reduction and oxidation responses are observed. The electrochemical reaction was diffusion-controlled, because the $I_p/{\upsilon}^{1/2}$ ratio was constant for the anodic and cathodic wave of thioxantone derivatives. These substituent effects are presented in terms of correlations of oxidation (or reduction) potentials with the highest occupied molecular orbital (HOMO), or lowest unoccupied molecular orbital (LUMO) energies, respectively. There is good correlation between energies of the HOMO vs. $E_{pa}^{(+)}$ and energies of the LUMO vs. $E_{pc}^{(-)}$. Frontier Molecular Orbital (FMO) is changed by the functional group of thioxanthones. FMO energy level was offered us the information about the electron transfer direction, and the coefficient of FMO was offered the information about the electron transfer position. Sulfur atom has an important effect on oxidation potential, $E_{pa}^{(+)}$ and the carbonyl carbon has an important effect on reduction potential, $E_{pc}^{(-)}$. Therefore we were appreciated that the contribution of sulfur atom for the $E_{pa}^{(+)}$ and HOMO energies is larger than the contribution of carbonyl group for the $E_{pc}^{(-)}$ and LUMO energies.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.853-858
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• 2003

The reaction mechanism of the pyrolysis of sulphonyl oximes ($CH_3-C_6H_4-S(O)_2O-N=C(H)-C_6H_4Y$), in the gas phase is studied theoretically at HF/3-21G, ONIOM (B3LYP/6-31G**:HF/3-21G) and ONIOM (MP2/6- 31G**:HF/3-21G) levels. All the calculations show that the thermal decomposition of sulphonyl oximes is a concerted asynchronous process via a six-membered cyclic transition state. The activation energies (Ea) predicted by ONIOM (B3LYP/6-31G**: HF/3-21G) method are in good agreement with the experimental results for a series of tosyl arenecarboxaldoximes. Five para substituents, Y = $OCH_3$, $CH_3$, H, Cl, and $NO_2$, are employed to investigate the substituent effect on the elimination reaction. Linear Hammett correlations are obtained in all calculations in contrast to the experimental finding.

• Bulletin of the Korean Chemical Society
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• v.7 no.3
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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.

• Journal of the Korean Chemical Society
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• v.7 no.3
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• pp.211-215
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• 1963

Inter-relationship between the Hammett equation and the linear enthalpy-entropy effect has been discussed by deriving a new set of equations; ${\Delta}{\Delata}H^{\neq}=a{\sigma}+b{\Delta}{\Delta}S^{\neq}$ and ${\Delta}{\Delta}F^{\neq}=a{sigma}+(b-T){\Delta}{\Delta}S^{\neq}$ where a = -1.36p. Theoretical analysis show that the Hammett, Leffler and Brown equations are special limited forms of these general equations. A necessary and sufficient test of substituent effect can thus be provided by the plot of $({\Delta}{\Delta}H^{\neq}-a{\sigma)$ versus ${\Delta}{\Delta}S^{\neq}$.

• Bulletin of the Korean Chemical Society
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• v.13 no.6
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• pp.595-599
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• 1992

The temperature dependence of C-13 chemical shifts are observed for the cyclooctanone arylhydrazones. The temperature-dependent chemical shifts for these derivatives are explained by postualating the existence of two equilibrating structures. In addition, the assignment between the $^{13}C$ signals of methylene carbon pairs can be done by application of the ${gamma}$ -substituent effect.

• Bulletin of the Korean Chemical Society
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• v.21 no.9
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• pp.882-890
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• 2000

Ab initio calculations are carried out on protonation equilibria of 5-memberedheteroaromatic aldehydes (5MHAs;heteroatom Y = NH, O, PH,and S and substituentZ = NH2, OCH3, SCH3, CH3, H, Cl, CHO, CN,NO2) at the $MP2}6-31G*$ level. Naturalbond orbital (NBO) analyses show that the optimal localized natural Lewis structures of the protonated aldehydes,(P), are ortho (C3) protonated (for Y = O, PH and S) and N-pro-tonated (for Y = NH) forms in contrast to the standard structural Lewis formula for aldehydes, (R). The delo-calizability of ${\pilone}-pairon$ the heteroatom $(n{\pi}(Y))$ is in the order Y = NH > O > S > PH. The transmission efficiency of (Z) substituent effects to the carbonyl moiety run parallel to the delocalizability of $n{\pi}(Y)$ for R,but is dominantly influenced by the cationic charge on $C{\alpha}(C{\alpha}+)$ for P, which is in the reverse order of thede-localizability of $n{\pi}(Y).$ The Hammett ${\rho}values$ for variation of Z in the protonation are determined by the dif-ference in the transmission efficiencies between Pand R stateat simple interpretation of their magnitude is not warranted. However,the magnitude of the gas-phase ${\rho}z+$ values decreases as the level ofcomputation is raised from RHF/3-21G* to RHF/6-31G* and to $MP2}6-31G*$ but increases again at the MP4SDQ/6-31G* level. Further decrease occurs when solvent effect (water) is accounted for by the SCRF method. Comparison of the SCRF ${\rho}z+values$ with those determined in the aqueous acid solution for Y = S and CHCH shows inadequacy of accounting for the solvent effects on the ${\rho}values$ by a continuum model. It is noteworthy that semiempirical calculations, especially theAM1 method, give even lower magnitude of the gas-phase ${\rho}values.

• Bulletin of the Korean Chemical Society
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• v.5 no.6
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• pp.226-230
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• 1984

LIS's of cis and trans-methyl-2-phenylcyclopropanecarboxylate, cis and trans-t-butyl-2-phenylcyclopropanecarboxylate, cis and trans-N,N-dimethylcyclopropanecarboxamide, trans-2-phenylcyclopropyl methyl ketone and trans-2-phenylcyclopropyl t-butyl ketone have been studied. The LIS's hold the McConnell-Robertson relation and are mainly influenced by the steric effect. LIS's of trans isomers are larger than those of cis isomers. In trans isomers, the LIS's decrease in the following order: methyl ketone > methyl ester > N,N-dimethyl amide > t-butyl ketone${\sim}$t-butyl ester.

• Journal of the Korean Applied Science and Technology
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• v.37 no.2
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• pp.250-259
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• 2020

The solubilization constant (K_s) was determined by the UV-Vis method to investigate the interaction between organic matter (solubilized substance) and surfactant in solubilization. Solubilization constants and thermodynamic functions, according to the hydrophobic interaction between organic mater (4-alkylanilines with different alkyl substituent length) and cationic surfactants (DTAB, TTAB, and CTAB, having different hydrophobic lengths), were measured and calculated at various temperatures and compared with each other. As a result, the hydrophobic interactions between organic matters and cationic micelles increased with increasing the chain length of solute's substituent as well as surfactant's hydrophobe. However, the hydrophobic effect by the alkyl substituent of organic matter was greater than the hydrophobic effect by the surfactant. In addition, the results of the calculated thermodynamic functions showed that 4-alkylaniline was solubilized at the deep place in the micelle and its solubilization was greatly dependent on both the hydrophobic effects of organic matter and surfactant. At the calculated iso-structural temperature, the difference between the maximum and minimum values was less than 1K within the experimental conditions.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4304-4308
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• 2011

Kinetic studies of the reactions of O,O-dimethyl Z-S-aryl phosphorothioates with X-benzylamines have been carried out in dimethyl sulfoxide at $85.0^{\circ}C$. The Hammett (log $k_2$ vs ${\sigma}_X$) and Br$\ddot{o}$nsted [log $k_2$ vs $pK_a$(X)] plots for substituent X variations in the nucleophiles are discrete with a break region between 4-Me and H, while the Hammett plots (log $k_2$ vs ${\sigma}_Z$) for substituent Z variations in the leaving groups are linear. The sign of the cross-interaction constant (${\rho}_{XZ}$) is positive for both the strongly and weakly basic nucleophiles. Greater magnitude of ${\rho}_{XZ}$ (= 2.54) value is observed with the weakly basic nucleophiles compared to with the strongly basic nucleophiles (${\rho}_{XZ}$ = 0.17). The deuterium kinetic isotope effects ($k_H/k_D$) involving deuterated benzylamines [$XC_6H_4CH_2ND_2$] are primary normal ($k_H/k_D$ > 1). The proposed mechanism is a stepwise with a rate-limiting leaving group expulsion from the intermediate involving a frontside nucleophilic attack with a hydrogen bonded, four-center-type transition state for both the strongly and weakly basic nucleophiles.

• Archives of Pharmacal Research
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• v.28 no.1
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• pp.16-21
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• 2005

We wanted to elucidate the reason why the trityloxymethyl substituent in $\gamma$-trityloxymethyl-$\gamma$­butyrolactone takes a sterically unfavorable specific conformation, and so we synthesized 5-trityloxymethyldihydrofuran-3-one, 3-(trityloxymethyl)-4-butanolide and 2-trityloxymethyl- tetrahy­drofuran and we then analyzed their conformation by $^{1}H-NMR$ analysis.