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변상용,백규철,한만소,조봉래 대한화학회 2016 Bulletin of the Korean Chemical Society Vol.37 No.6
Elimination reactions of (E)-2,4,6-(NO2) 3C6H2CHNOC(O)C6H4X (3) promoted by R2NH/R2NH2 + in 70 mol% MeCN (aq) have been studied. The reactions produced elimination products and exhibited second-order kinetics. The β and |βlg| values remained nearly the same for all leaving groups and bases. The results can be described by the negligible pxy interaction coefficient, pxy = ∂β/∂pK lg = ∂βlg/∂pK BH ≈ 0, which provides a strong support for the (E1cb)irr mechanism. For eliminations from (E)-ArCHNOC(O)C6H4X (1, 3) and (E)-2,4,6-(NO2)3C6H2CHNOAr′ (2, 3), the change of the β-aryl group (Ar) from 2,4-dinitrophenyl (1) to 2,4,6-trinitrophenyl (3) increased the rate by 270-fold without appreciable change in the transition state structure. On the other hand, the leaving group (OAr′) variation from benzoate (3) to 4-nitrophenoxy (2) induced a change in reaction mechanism from (E1cb)irr to E2. These results have been attributed to the cyclic transition state for the nitrile-forming eliminations involving the benzoate leaving group.
변상용,백규철,한만소,김병태,조봉래 대한화학회 2017 Bulletin of the Korean Chemical Society Vol.38 No.11
Ketene-forming elimination from C4H3(O)CH2C(O)OC6H3-2-X-4-NO2 (1) promoted by R2NH in MeCN has been studied. The reactions produced elimination products and exhibited second-order kinetics with Brönsted β = 0.51, and |βlg| = 0.47–0.53, indicating that the reaction proceeds by the E2 mechanism via an E2-central transition state. Comparison of β, |βlg|, ΔH≠, and ΔS≠ values for R2NH-promoted eliminations from ArCH2C(O)OC6H3-2-X-4-NO2 reveals that the transition-state structures for Ar = furyl and thienyl are similar and more symmetrical than that for Ar = Ph. This outcome has been attributed to the greater double bond stabilizing ability of the former than that of the latter.
편상용,백규철,한만소,조봉래 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.12
Nucleophilic substitution reactions of 5-XC4H2(S)C(O)OC6H3 -2-Y-4-NO2 (1) promoted by 4-Z-C6H4O −/4-Z-C6H4OH in 20 mol % dimethyl sulfoxide (DMSO)(aq) have been studied kinetically. The reactions exhibited second-order kinetics with βacyl = −2.52 to −2.83, ρ(x) = 2.81–3.16, βnuc = 0.88–0.04 and βlg = −0.94, respectively. The results have been interpreted with an addition–elimination mechanism in which the nucleophilic attack occurs in the rate-determining step. Comparison with existing data reveals that the rate-determining step changes from the second to the first step by the change in the nucleophile from R2NH/R2NH2 + to 4-Z-C6H4O −/4-Z-C6H4OH.
편상용,백규철,한만소,조봉래 대한화학회 2016 Bulletin of the Korean Chemical Society Vol.37 No.3
Nucleophilic substitution reactions of 5‐XC4H2 (S)C(O)OC6H3 ‐2‐Y‐4‐NO2 (1) promoted by 4‐Z‐C6H4O −/4‐Z‐C6H4OH in 20 mol % dimethyl sulfoxide (DMSO)(aq) have been studied kinetically. The reactions exhibited second‐order kinetics with βacyl = −2.52 to −2.83, ρ(x) = 2.81–3.16, βnuc = 0.88–0.04 and βlg = −0.94, respectively. The results have been interpreted with an addition–elimination mechanism in which the nucleophilic attack occurs in the rate‐determining step. Comparison with existing data reveals that the rate‐determining step changes from the second to the first step by the change in the nucleophile from R2NH/R2NH2 + to 4‐Z‐C6H4O −/4‐Z‐C6H4OH.
변상용,백규철,한만소,조봉래 대한화학회 2019 Bulletin of the Korean Chemical Society Vol.40 No.10
Reactions of 2,4-dinitrophenyl 2-thiophenecarboxylate (2a?d) with R2NH/R2NH2+ in 20?mol % DMSO(aq) have been studied. The reactions are overall second order, first order to the substrates, and first order to the nucleophiles. The Bronsted plots showed downward curves with pKa0 = 9.5, ?1 = 0.22?0.34, and ?2 = 0.85?0.92. The k1 values increased with a stronger electron-withdrawing 5-thienyl substituent and a stronger nucleophile, whereas the k2/k?1 values remained nearly the same for all 5-thienyl substituents. The influence of 5-thienyl substituent on the reaction rates showed excellent correlations on the Yukawa-Tsuno plots with ? = 1.28?2.16 and r = 0.20?0.60. The ? value increased and r value decreased with a stronger nucleophile, indicating an increase in the electron density at the carbonyl carbon and a decrease in the resonance demand. From these results, a stepwise mechanism with a change in the rate-determining step has been proposed.
변상용,백규철,한만소,홍승택,조봉래 대한화학회 2023 Bulletin of the Korean Chemical Society Vol.44 No.11
The kinetics of nucleophilic substitution reactions involving 2,4-dinitrophenyl 5-substituted-2-thiophenecarboxylate were studied kinetically with 4-ZC6H4O /4-Z-C6H4OH, which facilitated the reactions, in 20 mol% DMSO(aq). The reactions followed second-order kinetics and exhibited βacyl = 2.34 to 2.92, ρ(Y) = 2.71–3.39, βnuc = 0.74–0.83, and jβlgj = 0.40–0.57. Based on the interpretation of the results, we have concluded that the reaction follows an addition–elimination mechanism in which the first step is the rate-determining step (rds). The transition state structures for the 4-ZC6H4O-promoted reactions remained nearly the same with a change in the leaving group from 4-nitrophenoxide to 2,4-dinitrophenoxide. The mechanism of the 4-ZC6H4O- promoted reaction was similar to that of R2NH-promoted reactions, except that the former proceeded with the 1st step being the rds and the latter proceeded with a change in the rds from the second to the first step with a stronger nucleophile.
변상용,백규철,한만소,조봉래,Sang Yong Pyun,Kyu Cheol Paik,Man So Han,Bong Rae Cho 대한화학회 2023 대한화학회지 Vol.67 No.3
Acyl transfer reactions of 2,4-dinitrophenyl-5-substituted-2-furoates (1a-d) promoted by R<sub>2</sub>NH/R<sub>2</sub>NH<sub>2</sub><sup>+</sup> in 20mol% DMSO(aq) have been studied kinetically. The reactions are second-order and exhibit downward curves of the Brönsted plots with pK<sub>a</sub><sup>0</sup> = 9.5, β<sub>1</sub> = 0.23-0.35 and β<sub>2</sub> = 0.88-0.99. The k<sub>1</sub> values increased with a stronger nucleophile and as the electron-withdrawing ability of the 5-furyl substituent increases. In contrast, the k<sub>2</sub>/k<sub>-1</sub> values were nearly idential regardless of the 5-furyl substituents. From these results, a stepwise mechanism with a change in the rate-determining step(RDS) is proposed.