• Bulletin of the Korean Chemical Society
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• v.19 no.7
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• pp.776-779
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• 1998

Second-order rate constants have been measured spectrophotometrically for the addition reaction of a series of alicyclic amines to 3-butyn-2-one to yield their respective enamines at 25.0 'C. The reactivity of the amines increases with increasing the basicity of the amines. However, the Bronsted-type plot obtained exhibits a downward curvature as the basicity of the amines increases, i.e. βnuc decreases from 0.3 for low basic amines (pKa < 9) and to 0.1 for highly basic amines (pKa > 9). Such a curvature in the Bronsted-type plot is clearly indicative of a change in the reaction mechanism or transition state structure. From the corresponding reactions run in D2O, the magnitude of kinetic isotope effect (KIE) has been calculated to be about 0.8 for highly basic amines and 1.21 for weakly basic amines. The difference in the magnitude of KIE also supports a change in the reaction mechanism or transition state structure upon changing the basicity of the amines. Furthermore, the small KIE clearly suggests that H+ transfer is not involved in the rate-determining step, i.e. the addition reaction is considered to proceed via a stepwise mechanism in which the attack of the amines to the acetylene is the rate-determining step. The curvature in the Bronsted-type plot has been attributed to a change in the degree of bond formation between the amine and the acetylene.

• Bulletin of the Korean Chemical Society
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• v.24 no.9
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• pp.1245-1250
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• 2003

Pseudo-first-order rate constants ($k_{obs}$) have been measured spectrophotometrically for the reactions of 4-nitrophenyl benzoate with a series of pyridines in $H_2O$ containing 20 mol % DMSO. The plots of kobs vs pyridine concentration are linear up to ca. 0.1 M pyridines, indicating that the effect of self-association of pyridines with their conjugate acids are insignificant in this concentration range. The Bronsted-type plot has been obtained to be linear with a ${\beta}_{nuc}$ value 1.11, suggesting that the pyridinolyses proceed through a rate-determining breakdown of the zwiterionic addition intermediate. The pyridines studied have shown higher reactivity than isobasic primary and secondary amines toward the substrate. 1-Benzoyl-4-dimethylaminopyridinium ion, a possible intermediate, has not been detected since the rate of its hydrolysis in the reaction condition is comparable with or even faster than its formation.

• Journal of the Korean Chemical Society
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• v.19 no.3
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• pp.156-162
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• 1975

Rates of reactions of methanesulfonyl chloride with various substituted anilines have been measured in methanol. Substituent effects in aniline are found to be linearly correlated with pKa(Bronsted relation with ${\beta}$ = 0.84) and ${\rho}$(Hammett equation with ${\rho}$ = -2.46) respectively. The results are interpreted in terms of degree of bond-formation at the transition state, which was found to have progressed relatively further. The rates for o-methylaniline deviated from the Bronsted plot established by meta and para substituted anilines because of a steric effect of ortho position in aniline. Activation parameters, ${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$ have also been determined. The enthalpy of activation showed a regular variation in that electron donating substituents in the p-substituted aniline decrease ${\Delta}H^{\neq}$ and increase the negative value of ${\Delta}S^{\neq}$.

• Bulletin of the Korean Chemical Society
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• v.29 no.12
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• pp.2509-2512
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• 2008

• Bulletin of the Korean Chemical Society
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• v.18 no.5
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• pp.523-527
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• 1997

Apparent second-order rate constants (kapp) have been measured spectrophotometrically for the reaction of 2,4-dinitrophenyl benzoate (DNPB) with 6 secondary cyclic amines in H2O containing 20 mole% DMSO at 25.0±0.1 ℃. The Bronsted-type plot (log kapp vs. pKa) shows a break at pKa near 9.1, e.g. two straight lines with βapp values of 0.67 and 0.44 for the low basic (pKa < 9.1) and the highly basic (pKa > 9.1) amines, respectively. Using an estimated k2 value of 3×109 sec-1, all the other microconstants (k1, k-1 and K) involved in the present aminolysis have been calculated. The k value decreases with increasing the basicity of amines while k1 and K values increase with increasing the amine basicity, as expected. Good linear Bronsted-type plots have been obtained for these microconstants of the present aminolysis of DNPB. The magnitudes of the slope of the Bronsted-type plots, k1 and k-1 have been calculated to be 0.43 and - 0.24, respectively, indicating the k-1 step is about two folds less sensitive than the k1 step to the amine basicity. The K value has been calculated to be 0.66, which appears to be much smaller than the one for other aminolyses showing general base catalysis. The small K value has been attributed to the absence of general base catalysis in the present aminolysis of DNPB.

• Bulletin of the Korean Chemical Society
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• v.15 no.7
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• pp.585-589
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• 1994

Second-order rate constants have been measured spectrophotometrically for the nucleophilic substitution reactions of S-p-nitrophenyl thiobenzoate with various anionic nucleophiles including 6 ${\alpha}$-effect nucleophiles. A good Bronsted correlation has been observed for the reactions with 7 aryloxides. However, p-chlorothiophenoxide and hydroxide ions exhibit significantly positive and negative deviations, respectively, from the Bronsted plot. The deviations are attributed to the effect of polarizability and solvation rather than a change in the reaction mechanism. The ${\alpha}$-effect nuceophiles except highly basic ones demonstrate remarkably enhanced nucleophilicity. The effects of solvation and/or polarizability are proposed to be important for the cause of the ${\alpha}$-effect.

• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2455-2460
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• 2013

Second-order rate constants ($k_N$) have been measured spectrophotometrically for the nucleophilic displacement reactions of 4-nitrophenyl X-substituted-cinnamates (4a-4e) and Y-substituted-phenyl cinnamates (5a-5e) with Z-substituted-phenoxide anions in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Hammett plot for the reactions of 4a-4e with 4-chlorophenoxide (4-$ClPhO^-$) consists of two intersecting straight lines, which might be taken as a change in the rate-determining step (RDS). However, it has been concluded that the nonlinear Hammett plot is not due to a change in the RDS but is caused by stabilization of the ground state of substrates possessing an electron-withdrawing group in the cinnamoyl moiety through resonance interactions, since the Yukawa-Tsuno plot exhibits an excellent linear correlation with ${\rho}X=0.89$ and r = 0.58. The Br${\o}$nsted-type plot for the reactions of 4-nitrophenyl cinnamate (4c) with Z-substituted-phenoxides is linear with ${\beta}_{nuc}=0.76$. The Br${\o}$nsted-type plot for the reactions of Y-substituted-phenyl cinnamates (5a-5d) with 4-chlorophenoxides (4-$ClPhO^-$) is also linear with ${\beta}_{lg}=-0.72$. The Hammett plot correlated with ${\sigma}^-$ constants for the reactions of 5a-5d results in a much better linear correlation than that correlated with ${\sigma}^o$ constants, indicating that a partial negative charge develops on the O atom of the leaving aryloxide. Thus, the reactions have been concluded to proceed through a concerted mechanism.

• Journal of the Korean Chemical Society
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• v.40 no.12
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• pp.733-740
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• 1996

The rate constants for the hydrolysis of 4'-[N-(9-acridinyl)]-1'-(N-methanesulfonyl)-3'-methoxyquinonediimide(AMQD) were determined by ultraviolet visible spectrophotometer in water at $25^{\circ}C.$ The rate equation which could be applied over wide pH ranges were obtained. On the basis of pH-rate profile, Bronsted plot, hydrolysis product analysis, general base catalysis and substituent effect, the plausible hydrolysis mechanism was proposed: Below pH 3.00, the hydrolysis reaction was proceeded by the attack of water to 4'-position of quinonoid after protonation at nitrogen of acridinyl and between pH 3.00 and 9.00, the addition of water and hydroxide occurred competitively. However, above pH 9.00, the rate constants were dependent upon only the concentration of hydroxide ion.

• Journal of the Korean Chemical Society
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• v.23 no.1
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• pp.37-41
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• 1979

The kinetics of the reaction of benzyl m-nitrobenzenesulfonate with m-and p-substituted N,N-dimethylanilines in acetone have been investigated by an electric conductivity method. The effects of substituents on the reactivity of N,N-dimethylaniline and the existence of linear free energy relationship were discussed. The rate constants k were in the range 2.55∼487 $10^{-4}l{\cdot}mol^{-l}{\cdot}sec^{-1} (35^{\circ}C)$ and increased with the electron donating ability of substituents. In the present reaction, the Hammett plot was correlated with ${\sigma}$ substituent constant, especially using the new ${\sigma}$ value of 0.35 in p-MeO and it's ${\rho}$ value was found to be -1.37. r value for the reaction was very large than the value obtained in the reaction of benzyl bromide. $Br{\"{o}}nsted$ linear relationship was shown between rate constant and basicites except for p-MeO resulted from solvent effect. From the Bronsted plot, this reaction was suggested that the cleavage of the C${\cdot}{\cdot}{\cdot}$O bond in the $S_N2$ transition state proceed the bond formation.

• Bulletin of the Korean Chemical Society
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• v.28 no.10
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• pp.1797-1802
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• 2007

The kinetics and mechanism of the nucleophilic substitution reactions of diphenyl phosphinic (1) and thiophosphinic (2) chlorides with substituted X-pyridines are investigated kinetically in acetonitrile at 35.0 and 55.0 oC, respectively. A concerted mechanism with backside nucleophilic attack is proposed for the pyridinolysis of 1, on the basis of the linear Bronsted plot with the βX value of 0.68. In the case of the pyridinolysis of 2, the Hammett and Bronsted plots are biphasic concave upwards with the break point at 3- phenyl pyridine. These results indicate a change in mechanism from a concerted SN2(P) process with direct backside nucleophilic attack for less basic nucleophiles (X = 3-CN-3-Ph) to a stepwise process with frontside attack for more basic nucleophiles (X = 4-MeO-3-Ph). Apparent secondary inverse kinetic isotope effects with deuterated pyridine (C5D5N), kH/kD < 1, are observed for the pyridinolysis of 1 and 2.