• Journal of the Korean Chemical Society
• /
• v.24 no.6
• /
• pp.413-420
• /
• 1980

Die Geschwindigkeitskonstanten der Solvolyse-Reaktionen von 9-Chlormethylanthracen wurden bei verschiedenen Temperaturen in unterschiedlichen binadren Losungsmittelgemischen (Wasser/Aceton, Wasser/Acetonitril, Wasser/Methanol, Wasser/Athanol) mit Hilfe der Leitfahigkeitsmeßungen bestimmt. Die Aktivierungsparameter $E_a$, ${\Delta}H^{\neq}$ und ${\Delta}S^{\neq}$ wurden berechnet. Die Meßergebnisse deuten darauf hin, daß die Solvolyse von 9-Chlormethylanthracen in protonischen Losungsmitteln schneller ablauft als in aprotonischen Losungsmitteln; in den Meßreihen mit protonsichen bzw. mit aprotonischen Losungsmitteln steigt die Reaktionsgeschwindigkeit mit der Zunahme der Dielektrizitatskonstanten des Losungsmittels an, und die Aktivierungsparameter nehmen mit steigendem Wassergehalt zu. Es wurde festgestellt, daß die Reaktion nach einem $S_N1$-Mechanismus ablauft. Die experimentellen Daten deuten darauf hin, daß Wasser einerseits als Nucleophil und andererseits als allgemeine Base am Reaktionsmechanismus beteiligt ist.

• Journal of Microbiology and Biotechnology
• /
• v.12 no.1
• /
• pp.149-152
• /
• 2002

The effect of pressure on the catalytic properties of glutamate racemase from Aquifex pyrophilus, an extremophilic bacterium, was investigated. The activation volume for the overall reaction $({\Delta}V^{\neq})$ and catalysis $({{Delta}V_{cat}}^{\neq})$ was -96.97 ml/mol and 4.97 ml/mol, respectively, while the reaction volume for the substrate binding (${\Delta}V_{K_m^-1}$) was -101.94 ml/mol. The large negative ${\Delta}V^{\neq}$ for the overall reaction indicated that the pressurization of glutamate racemase resulted in enhanced catalytic efficiencies. In addition, this value was also due to the large negative ${Delta}V_{K_m^-1}$ for the substrate binding. The negative value of ${Delta}V_{K_m^-1}$ implied that the conformational changes in the enzyme molecule occurred during the substrate binding process, thereby increasing the degree of hydration. The small value of ${{Delta}V_{cat}}^{\neq}$suggested that the pressure did not affect the glutamate racemase catalysis after the substrate binding.

• Journal of the Korean Chemical Society
• /
• v.9 no.1
• /
• pp.23-28
• /
• 1965

Halogen exchanges between benzyl chloride and chloride ion have been studied in 90% ethanol-water mixture, and activation parameters in the exchange reaction have been determined; ${\Delta}H^{\neq}$ = 18. 50 Kcal and ${\Delta}S^{\neq}$ = -22. 09 e. u. Results indicated that the reaction proceeded via a typical bimolecular mechanism. The importance of nucleophilic ability of attacking anion in $S_N2$ process has been stressed giving some experimental evidence. The order of reactivity of halides in the exchange reaction is better explained with the Swain's nucleophilic parameter than with the bond dissociation energies.

• Journal of applied mathematics & informatics
• /
• v.5 no.3
• /
• pp.819-826
• /
• 1998

The purpose of this paper is to prove the following results; (1) Let R be a prime ring of char $(R)\neq 2$ and I a nonzero left ideal of R. The existence of a nonzero symmetric bi-derivation D : $R\timesR\;\longrightarrow\;$ such that d is sew-commuting on I where d is the trace of D forces R to be commutative (2) Let m and n be integers with $m\;\neq\;0.\;or\;n\neq\;0$. Let R be a noncommutative prime ring of char$ (R))\neq \; 2-1\; p_1 \;n_1$ where p is a prime number which is a divisor of m, and I a nonzero two-sided ideal of R. Let $D_1$ ; $R\;\times\;R\;\longrightarrow\;and\;$ $D_2\;:\;R\;\times\;R\;longrightarrow\;R$ be symmetric bi-derivations. Suppose further that there exists a symmetric bi-additive mapping B ; $R\;\times\;R\;\longrightarrow\;and\;$ such that $md_1(\chi)\chi ＋ n\chi d_2(\chi)=f(\chi$) holds for all $\chi$$\in$I, where $d_1 \;and\; d_2$ are the traces of $D_1 \;and\; D_2$ respectively and f is the trace of B. Then we have $D_1=0 \;and\; D_2=0$.

• Journal of the Korean Chemical Society
• /
• v.16 no.5
• /
• pp.290-297
• /
• 1972

We have obtained the results of Cannizzaro reaction of furfural, 5-methylfurfural and 5-bromofurfural by using alcoholic potassium hydroxide solution in 95% (V/V) methanol solvent at $0{\sim}40^{\circ}C$. The results are as follows: 1) Their Cannizzaro reaction is fourth-order reaction, and the reaction of furfural proceeds 3 times as rapid as that of 5-methylfurfural and 10 times as slow as that of 5-bromofurfural. 2) Their activation energies of furfural, 5-methylfurfural and 5-bromofurfural in the reaction are 10.46Kcal/mole, 16.27Kcal/mole, and 9.62Kcal/mole respectively, and the calculated activation parameters, and ${\Delta}S^{\neq}$, increase in the order of 5-bromofurfural, furfural and 5-methyl-furfural.

• Journal of the Korean Chemical Society
• /
• v.7 no.4
• /
• pp.264-270
• /
• 1963

The general equation for the substituent effect test, which was derived in the previous paper, has been extended to correlate thermodynamic parameters of solvolysis reaction by modifying the potential energy term to represent the effect of changes in solvent composition. The linear fits of the new equation, $\Delta{\Delta}H^\neq=a'Y+b\Delta{\Delta}S^\neq$, were tested with 35 examples from literature and average correlation coefficient of 0.977 was obtained. Examination of results showed that the equation is generally applicable to solvolysis reaction and helps elucidate some the difficulties experienced with the Grunwald-Winsteln equation. It has been stressed that the linear enthalpy-entropy effect exists only between the external enthalpy and entropy of activation, and therefore strictly it is the linear external enthalpy-entropy effect.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.12
• /
• pp.4347-4351
• /
• 2011

The nucleophilic substitution reactions of ethylene phosphorochloridate (2) with X-pyridines are investigated kinetically in acetonitrile at $-20.0^{\circ}C$. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. Unusual positive ${\rho}_X$ (= +2.49) and negative ${\beta}_X$ (= -0.41) values are obtained with the weakly basic pyridines, and rationalized by the isokinetic relationship with isokinetic temperature at $t_{ISOKINETIC}=6.6^{\circ}C$. The pyridinolysis rate of 2 with a cyclic five-membered ring is forty thousand times faster than its acyclic counterpart (3: diethyl chlorophosphate) because of great positive value of the entropy of activation of 2 (${\Delta}S^{\neq}$ = +49.2 eu) compared to negative value of 3 (${\Delta}S^{\neq}$ = -44.1 eu) over considerably unfavorable enthalpy of activation of 2 (${\Delta}H^{\neq}=28.4\;kcal\;mol^{-1}$) compared to 3 (${\Delta}H^{\neq}=6.3\;kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.1
• /
• pp.270-274
• /
• 2012

The nucleophilic substitution reactions of 1,2-phenylene phosphorochloridate (1c) with X-pyridines are investigated kinetically in acetonitrile at $-25.0^{\circ}C$. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Ph. The pyridinolysis rate of 1c with a cyclic five-membered ring is $2.70{\times}10^5$ times faster than its acyclic counterpart (1a: phenyl ethyl chlorophosphate) because of great positive value of the entropy of activation of 1c (${\Delta}S^{\neq}$ = +26 eu) compared to negative value of 1a (${\Delta}S^{\neq}$= -24 eu) over considerably unfavorable enthalpy of activation of 1c (${\Delta}H^{\neq}=20.5kcal\;mol^{-1}$) compared to 1a (${\Delta}H^{\neq}=12.7kcal\;mol^{-1}$). Great enthalpy and positive entropy of activation are ascribed to sterically congested transition state (TS) and solvent structure breaking in the TS. A concerted mechanism involving a change of nucleophilic attacking direction from a frontside attack with the strongly basic pyridines to a backside attack with the weakly basic pyridines is proposed on the basis of greater selectivity parameters (${\rho}_X$ = -1.99 and ${\beta}_X$ = 0.41) with the strongly basic pyridines compared to those (${\rho}_X$ = -0.42 and ${\beta}_X$ = 0.07) with the weakly basic pyridines.

• Journal of the Korean Chemical Society
• /
• v.17 no.6
• /
• pp.406-410
• /
• 1973

Kinetic study of halide exchange for dimethylsulfamoyl chloride in dry acetone by using radioisotopic halide ions has been carried out at two temperatures. The result of the order of nucleophilicity, as compared with benzenesulfonyl chloride, shows a similar tendency but reaction rate is slower, more than $10^{-2}$times, than benzenesulfonyl chloride. The activation parameter, ${\Delta}H^{\neq}\;and\;{\Delta}S^{\neq}$ decrease in sequence $Cl^-\;>\;Br^-\;>\;I^-$ in dimethylsulfamoyl chloride but it is the reverse order found for benzenesulfonyl chloride. The results are interpreted with bond-breaking, bond-formation, and electronic requirments, and in the light of HSAB Principle.

• Journal of the Korean Chemical Society
• /
• v.30 no.4
• /
• pp.377-382
• /
• 1986

Racemic tris-oxalatocobaltate (III) complex ions were optically resolved by an optical active complex, ${\Delta}$-tris-ethylenediamine cobalt (III), and then racemization of ${\bigwedge}-[Co(ox)_3]^{3-}$ obtained was investigated in various mixed solvent such as water-organic solvent (organic solvents=ethanol, iso-propyl alcohol, acetone, and dioxane). The rate of racemization was increased with following order; water < ethanol < acetone < isopropyl alcohol < dioxane; which is the same order for polarizability of organic solvent added. Considering ${\Delta}H^{\neq},\;{\Delta}S^{\neq}$ and above facts for the racemization of ${\bigwedge}-[Co(ox)_3]^{3-}$, it seems to be twist mechanism of plausible mechanisms.