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RISS 인기검색어
- 검색키워드
- 저자 : Kevill, (검색결과 29 건)
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고한중,강석진,Dennis N. Kevill 대한화학회 2008 Bulletin of the Korean Chemical Society Vol.29 No.10
Rate of solvolysis of diphenylthiophosphinyl chloride in ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone, 2,2,2-trifluoroethanol (TFE) or 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) are reported. Solvolyses were also carried out in TFE-ethanol mixtures. For five representative solvents, studies were made at several temperatures and activation parameters determined. The 29 solvents gave a reasonably precise extended Grunwald-Winstein equation plot, correlation coefficient (R) of 0.933, which improved to 0.983 when the four TFE-ethanol points were excluded. The sensitivities (l = 1.00 and m = 0.64) were similar to those obtained for dimethyl phosphorochloridate and phosphorochloridothionate and diphenylphosphinyl chloride (1). As with the four previously studied solvolyses, an SN2 pathway is proposed for the solvolyses of diphenylthiophosphinyl chloride. The activation parameters, ΔH≠ and ΔS≠, were determined and they are also in line with values expected for an SN2 reaction.
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Kinetic and Theoretical Consideration of 3,4- and 3,5-Dimethoxybenzoyl Chlorides Solvolyses
Park, Kyoung-Ho,Kevill, Dennis N. Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.10
The solvolysis rate constants of 3,4- (1) and 3,5-dimethoxybenzoyl (2) chlorides were measured in various pure and binary solvents at $25.0^{\circ}C$, and studied by application of the extended Grunwald-Winstein (G-W) equation, kinetic solvent isotope effect in methanolysis and activation parameters. The solvolysis of 1 was interpreted as the unimolecular pathway due to a predominant resonance effect from para-methoxy substituent like 4-methoxybenzoyl chloride (3), while that of 2 was evaluated as the dual mechanism, with unimolecular or bimolecular reaction pathway according to the character of solvent systems (high electrophilic/nucleophilic) chosen, caused by the inductive effect by two meta-methoxy substituents, no resonance one. In the solvolyses of 1 and 2 with two $-OCH_3$ groups, the resonance effect of para-methoxy substituent is more important to decide the mechanism than the inductive effect with other corresponding evidences.
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Kinetic and Theoretical Consideration of 3,4- and 3,5-Dimethoxybenzoyl Chlorides Solvolyses
박경호,Dennis N. Kevill 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.10
The solvolysis rate constants of 3,4- (1) and 3,5-dimethoxybenzoyl (2) chlorides were measured in various pure and binary solvents at 25.0 oC, and studied by application of the extended Grunwald-Winstein (G-W) equation, kinetic solvent isotope effect in methanolysis and activation parameters. The solvolysis of 1 was interpreted as the unimolecular pathway due to a predominant resonance effect from para-methoxy substituent like 4- methoxybenzoyl chloride (3), while that of 2 was evaluated as the dual mechanism, with unimolecular or bimolecular reaction pathway according to the character of solvent systems (high electrophilic/nucleophilic) chosen, caused by the inductive effect by two meta-methoxy substituents, no resonance one. In the solvolyses of 1 and 2 with two –OCH3 groups, the resonance effect of para-methoxy substituent is more important to decide the mechanism than the inductive effect with other corresponding evidences.
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A Kinetic Study on Solvolysis of Diphenyl Thiophosphorochloridate
고한중,강석진,Dennis N. Kevill 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.2
Rates of solvolyses of diphenyl thiophosphorochloridate ((PhO)2PSCl, 1) in ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone and 2,2,2-trifluoroethanol (TFE) are reported. For four representative solvents, studies were made at several temperatures and activation parameters were determined. The 30 solvents gave a reasonably precise extended Grunwald-Winstein plot, correlation coefficient (R) of 0.989. The sensitivity values (l = 1.29 and m = 0.64) of diphenyl thiophosphorochloridate ((PhO)2PSCl, 1) were similar to those obtained for diphenyl phosphorochloridate ((PhO)2POCl, 2), diphenylphosphinyl chloride (Ph2POCl, 3) and diphenylthiophosphinyl chloride (Ph2PSCl, 4). As with the previously studied of 3~4 solvolyses, an SN2 pathway is proposed for the solvolyses of diphenyl thiophosphorochloridate (1). The activation parameters, ΔH≠ (= 11.6~13.9 kcal․mol-1) and ΔS≠ (= -32.1 ~ -42.7 cal․mol-1․K-1), were determined, and they were in line with values expected for an SN2 reaction. The large kinetic solvent isotope effects (KSIE, 2.44 in MeOH/MeOD and 3.46 in H2O/D2O) are also well explained by the proposed SN2 mechanism.
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Kinetic Studies of the Solvolyses of 2,2,2-Trichloro-1,1-Dimethylethyl Chloroformate
고한중,강석진,Dennis N. Kevill 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.4
The rate constants of solvolyses of 2,2,2-trichloro-1,1-dimethylethyl chloroformate (I) in 33 solvents can be well correlated using the extended Grunwald-Winstein equation, with incorporation of the NT solvent nucleophilicity scale and the YCl solvent ionizing scale, with sensitivities towards changes in the scale having values of 1.42 ± 0.09for l and 0.39 ± 0.05 for m, respectively. The activation enthalpies are ΔH≠ = 12.3 to 14.5 kcal·mol‒1 and the activation entropies are ‒28.2 to ‒35.5 cal·mol‒1·K‒1, consistent with the proposed bimolecular reaction mechanism. The kinetic solvent isotope effect of 2.14 in MeOH/MeOD is in accord with a bimolecular mechanism, probably assisted by general-base catalysis.
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A Kinetic Study on Solvolysis of Diphenyl Thiophosphorochloridate
Koh, Han-Joong,Kang, Suk-Jin,Kevill, Dennis N. Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.2
Rates of solvolyses of diphenyl thiophosphorochloridate ($(PhO)_2$PSCl, 1) in ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone and 2,2,2-trifluoroethanol (TFE) are reported. For four representative solvents, studies were made at several temperatures and activation parameters were determined. The 30 solvents gave a reasonably precise extended Grunwald-Winstein plot, correlation coefficient (R) of 0.989. The sensitivity values (l = 1.29 and m = 0.64) of diphenyl thiophosphorochloridate ($(PhO)_2$PSCl, 1) were similar to those obtained for diphenyl phosphorochloridate ($(PhO)_2$POCl, 2), diphenylphosphinyl chloride ($Ph_2$POCl, 3) and diphenylthiophosphinyl chloride ($Ph_2$PSCl, 4). As with the previously studied of 3~4 solvolyses, an $S_N$ pathway is proposed for the solvolyses of diphenyl thiophosphorochloridate (1). The activation parameters, ${\Delta}H^{\neq}\;(=11.6{\sim}13.9\;kcal{\cdot}mol^{-1})\;and\;{\Delta}S^{\neq}\; (=\;-32.1\;{\sim}\;-42.7\;cal{\cdot}mol^{-1}{\cdot}K^{-1})$, were determined, and they were in line with values expected for an $S_N$2 reaction. The large kinetic solvent isotope effects (KSIE, 2.44 in MeOH/MeOD and 3.46 in $H_2O/D_2$O) are also well explained by the proposed $S_N$2 mechanism.
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Koh, Han-Joong,Kang, Suk-Jin,Kevill, Dennis N. Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.10
Rate of solvolysis of diphenylthiophosphinyl chloride in ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone, 2,2,2-trifluoroethanol (TFE) or 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) are reported. Solvolyses were also carried out in TFE-ethanol mixtures. For five representative solvents, studies were made at several temperatures and activation parameters determined. The 29 solvents gave a reasonably precise extended Grunwald-Winstein equation plot, correlation coefficient (R) of 0.933, which improved to 0.983 when the four TFE-ethanol points were excluded. The sensitivities (l = 1.00 and m = 0.64) were similar to those obtained for dimethyl phosphorochloridate and phosphorochloridothionate and diphenylphosphinyl chloride (1). As with the four previously studied solvolyses, an $SN_2$ pathway is proposed for the solvolyses of diphenylthiophosphinyl chloride. The activation parameters, ${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$, were determined and they are also in line with values expected for an $S_N2$ reaction.
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이용우,Mi Hye Seong,경진범,Dennis N. Kevill 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.11
The specific rates of solvolysis of t-butyl fluoroformate (1) have been measured at 40.0 oC in 21 pure and binary solvents. These give a satisfactory correlation over the full range of solvents when the extended Grunwald-Winstein equation, with incorporation of the solvent nucleophilicity and the solvent ionizing power, is applied. The actual values are very similar to those obtained in earlier studies of the solvolyses of isopropyl chloroformate and ethyl chlorothioformate in the more ionizing and least nucleophilic solvents, which are believed to proceed by an ionization pathway. The small negative values for the entropies of activation are consistent with the ionization nature of the proposed rate-determining step. These observations are also compared with those previously reported for the corresponding primary and secondary alkyl haloformate esters.
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경진범,Mi Hye Seong,김동국,Dennis N. Kevill 대한화학회 2008 Bulletin of the Korean Chemical Society Vol.29 No.9
Reactions of n-propyl fluoroformate in a variety of pure and binary solvents have been studied at 40.0 oC. The extended (two-term) Grunwald-Winstein equation has been applied to the specific rates of solvolysis of npropyl fluoroformate. The sensitivities (l = 1.80 ± 0.17 and m = 0.96 ± 0.10) to changes in solvent nucleophilicity and solvent ionizing power and the kF/kCl values are similar to those for solvolyses of n-octyl fluoroformate over the full range of solvents, suggesting that the addition step of an addition-elimination mechanism is ratedetermining. These observations are also compared with those previously reported for the corresponding chloroformate and fluoroformate esters.
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