• Journal of the Korean Chemical Society
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• v.17 no.1
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• pp.1-9
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• 1973

The purpose of this paper is to investigate the mechanism of Diels-Alder reaction by assuming pseudo molecular complex (PMC) which has characters both of ionic and radical bonds. We treated this complex quantum-chemically as an intermediate between the configuration without charge transfer (radical bond character) and the configuration corresponding to the charge transfer from Diene (R) to Dienophile (S) (ionic bond character). The wave function for the complex could be expressed as: ${\psi}_{complex} = {\psi}(R,S) +{ \rho}{\psi}(R^+,S^-)$ where ${\rho}$ is the extent of charge transfer which is a constant to measure the ionic character of PMC. It has been noticed that${\rho}$is related to the difference between Fr + Fr' and Fs + Fs' in free valence (F) when R is united to S through atom r in R to atom s in S and atom r' in R to atom s' in S, That is, ${\rho}{\alpha}$ ${\Delta}F = (Fr + Fr') - (Fs + Fs')$. We have calculated ${\Delta}F$values for more than forty Diels-Alder reactions. The calculated values of ${\Delta}F$ is reversely proportional to the values of Brown's paralocalization energy (Lp) as well as Dewar's differences of delocalization energy$({\Delta}Edeloc.)$ with good linearity. This approach also presents a way of predicting the possibility and the easiness of diene synthesis between any two conjugate compounds. According to the considerations, it could be concluded that Diels-Alder reaction takes place through the united ionic-radical mechanism rather than the separated ionic or radical mechanism.

• Elastomers and Composites
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• v.55 no.1
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• pp.51-58
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• 2020

In this study, the thermal oxidation of raw natural rubber (NR) was investigated under controlled conditions by optical image and fourier transform infrared (FT-IR) analysis. The thermal oxidation was performed on a transparent thin film of raw NR coated on a KBr window in a dark chamber at 80℃ under low humidity conditions to completely exclude moisture and restrict light oxidation. Images of the thin film of raw NR were obtained before and after thermal oxidation. FT-IR absorption spectra were measured in the transmission mode at different thermal exposure times. The thermal oxidation of NR was examined by the changes in the absorption peaks at 3449, 1736, 1447, 1377, 1242, 1072, and 833 cm^-1, which corresponded to a hydroxyl group (-OH), a carbonyl group (-C=O) from an aldehyde and a ketone, a methylene group (-CH₂-), a methyl group (-CH₃), a carbon-oxygen single bond (-C-O) from an epoxide, a carbon-oxygen bond (-C-O) from an ether, an alcohol, a peroxide, or a cyclic peroxide, and a cis-methine group (cis-CCH₃=CH-), respectively. In the initial stage of thermal oxidation, two different types of free radicals were produced quickly and randomly by the homolytic cleavage of a double bond and allylic hydrogen abstraction. Aldehydes and ketones were formed from chain scissions of the double bonds and alcohols were produced from allylic hydrogen abstraction at the methylene or methyl groups. Two reactions seemed to proceed competitively with each other. At a later stage, oxidative crosslinks seemed to dominate through the combination of free radicals such as an allyl radical (CH=CHCH₂·), alkoxy radical (RO·), and peroxy radical (ROO·) and the reaction of a hydroperoxide (-ROOH) with a double bond. The image obtained after thermal oxidation showed hardening without cracks. Based on these observations, a plausible two-step mechanism was suggested for chain hardening caused by the thermal oxidation.

• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.1939-1944
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• 2011

The nucleophilic substitution reactions of bis(Y-aryl) chlorophosphates (1) with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at 35.0 $^{\circ}C$. The kinetic results of 1 are compared with those of Y-aryl phenyl chlorophosphates (2). The substrate 1 has one more identical substituent Y compared to substrate 2. The cross-interaction between Y and Y, due to additional substituent Y, is significant enough to result in the change of the sign of cross-interaction constant (CIC) from negative ${\rho}_{XY}$ = -1.31 (2) to positive ${\rho}_{XY}$ = +1.91 (1), indicating the change of reaction mechanism from a concerted $S_N2$ (2) to a stepwise mechanism with a rate-limiting leaving group departure from the intermediate (1). The deuterium kinetic isotope effects (DKIEs) involving deuterated anilines ($XC_6H_4ND_2$) show secondary inverse, $k_H/k_D$ = 0.61-0.87. The DKIEs invariably increase as substituent X changes from electron-donating to electron-withdrawing, while invariably decrease as substituent Y changes from electron-donating to electron-withdrawing. A stepwise mechanism with a rate-limiting bond breaking involving a predominant backside attack is proposed on the basis of positive sign of ${\rho}_{XY}$ and secondary inverse DKIEs.

• Bulletin of the Korean Chemical Society
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• v.30 no.12
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• pp.2909-2912
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• 2009

The amines studied in this study are less reactive toward ethyl propiolate (3) in MeCN than in H$_2$O although they are 7 to 9 pK$_a$ units more basic in the aprotic solvent. The reactivity of morpholine and deuterated morpholine toward 3 is found to be identical, indicating that proton transfer occurs after rate-determining step (RDS). The fact that kinetic isotope effect is absent excludes a stepwise mechanism in which proton transfer occurs in RDS as well as a concerted mechanism in which nucleophilic attack and proton transfer occur concertedly through a 4-membered cyclic transition state (TS). Thus, the reactions have been concluded to proceed through a stepwise mechanism in which proton transfer occurs after RDS. Brønsted-type plots are linear with small ${\beta}_{nuc}$ values, i.e., ${\beta}_{nuc}$ = 0.29 in H$_2$O and ${\beta}_{nuc}$ = 0.51 in MeCN, indicating that bond formation is not advanced significantly in RDS. The small ${\beta}_{nuc}$ value also supports the conclusion drawn from the study of kinetic isotope effect.

• Journal of the Korean Chemical Society
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• v.55 no.5
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• pp.741-745
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• 2011

Well-resolved vibronic emission spectra were recorded in the visible region from the corona discharge of precursor alkylbenzenes in a technique of corona excited supersonic expansion using a pinhole-type glass nozzle. From the observed spectra, we found the evidence of the presence of benzyl-type radicals generated by dissociation of C-C or C-H bonds of alkyl group. After identification of benzyl-type radicals formed in the corona discharge, we suggest that energy densities in alkyl chain play a crucial role in determining the bond dissociation during corona excitation.

• The Microorganisms and Industry
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• v.13 no.1
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• pp.4-9
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• 1987

The regulation of gene expression in procaryotes is accomplished primarily at the level of transcription. Initiation of transcription is subject to numerous promoter-specific controls which act to ensure coordinate expression of disparate genes. The kinetics of formation of a functional("open") complex at a promoter, prior to the catalytic steps of RNA chain initiation and elongation, is thought to play a major role in controlling the efficiency of transcription of that promotor, since the subsequent processes of nucleotide binding and phosphodiester bond formation are rapid and are not promoter-specific (Mangel and Chamberlin, 1974 Shimamoto et al., 1981)

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2003.11a
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• pp.449-450
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• 2003

Performance of photochemical models and their response to emission controls are heavily dependent on the inputs to the model. Two key inputs to these models are accurate meteorological and emissions data. But they can contain significant errors which contribute to uncertainties in photochemical simulation (Kumar and Russell, 1996; Sistla et al., 1996; Pielke and Uliase, 1998; Barna and Lamb, 2000; Nelson L. Seaman, 2000: Hogrefe et al., 2001; Biswas et al., 2001).(omitted)

• Bulletin of the Korean Chemical Society
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• v.16 no.4
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• pp.310-315
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• 1995

The heterobimetallic anion, (OC)5CrMn(CO)5-M+ (M+=Na+, PPN+), which has a donor-acceptor metal-metal bond1, was reacted with allyl bromide to yield BrCr(CO)5- and Mn(CO)5(CH2CHCH2). The reaction mechanism has been proposed in terms of the consecutive reaction pathway in which Cr(CO)5(THF) is an important intermediate leading to the corresponding product. Counterion effect on this reaction was also evaluated and the results were compared with those of the corresponding reaction of the mononuclear carbonyl anion, Mn(CO)5-.

• The Korean Journal of Financial Management
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• v.20 no.2
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• pp.1-39
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• 2003

Using a comprehensive sample of convertible security offerings by Korean firms from 1981 to 1999, we examine the effect of convertible bond issues on firm value. We find that the announcement of convertible bond issues has a positive effect on firm value. However, the announcement of private convertible bond issues by chaebol firms has a significant negative effect on their market values. This result is different from that in Japan, suggesting that the efficiency of the financing decision by Korean chaebol is different from that by Japanese keiretsu. In addition, we find that the announcement effect of private convertible bond issues by chaebol firms has a significant relation with the corporate governance variables such as ownership structure, bank relationship. These results indicate that convertible bond issues can be used as a mechanism for chaebol owner-manager to give rise agency problems at the expense of the wealth of minority shareholders.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.333-339
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• 2007

The purpose of this study was to enhance bond performance between recycled PET (polyethylene telephthalat) fiber and cement composites through hydrophilic treatment using maleic anhydride grafted polypropylene(mPP). The mPP with various concentration of 0%, 5%, 10%, 15% and 20% to determine effect on bond behavior of recycled PET fiber were applied as experimental variables. Dog bone shaped specimens according to JCI SF-8 was applied to evaluate the bond strength and pullout energy. The results showed increased bond strength and pullout energy as concentration of mPP. Concentration of 15% mPP showed the most effective results while 20% showed reduced performance results. Because 15% mPP ensures perfect coating while 20% makes thick coating area that resulted in crack propagation and consequent separation of PET fiber and coated area during pullout load occurred. Enhancement mechanism of bond performance of recycled PET fiber and cement composites with each concentration of mPP could be conformed through investigation of microstructure of fiber surface.