• 대한화학회지
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• 제41권12호
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• pp.666-671
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• 1997

Pseudosaccharin pyridinemethyl ether들의 광화학반응을 검토하였다. Pseudosaccharin 2-pyridinemethyl ether, pseudosaccharin 4-pyridinemethyl ether, pseudosaccharin 3-pyridinemethyl ether 모두 빛조사에 의해 신속히 반응하였으며 반응은 pseudosaccharyl 산소원자와 pyridinemethyl 탄소원자 사이의 결합 균형분해과정과 용매로 사용한 메탄올에 의한 pyridinemethoxy기의 들뜬상태 친핵성 치환과정을 거쳐 진행됨을 관찰하였다. 이들 두 과정은 반응용액 중에 존재하는 산소분자에 의해 소멸되지 않았다. 광생성물 수율로 볼 때 결합균형분해과정이 들뜬상태 친핵성 치환과정 보다 우세함을 알았다.

• 대한화학회지
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• 제31권2호
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• pp.123-132
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• 1987

반경험적 분자궤도함수법인 MNDO방법을 사용하여 $SH^-,\;CN^-$ 그리고 $OH^-$와 메틸티오시아네이트(MTC)의 친핵성치환반응을 연구하였다. 각 친핵체에 대해 MTC세반응중심의 계산된 포텐샬에너지곡면(Intrinsic term)과 전이상태에서의 친핵체의 음전하크기(Solvent term)을 고려하여 가스상과 용액상에 대한 선택성을 논의하였다. 결과로써$SH^-$에 대해서는 선택성의 두 성분 모두 4-methylbenzylthiocyanate (4-MBTC)에 대해 얻어진 실험결과와 일치한반면 $CN^-$의 경우에는 고유항(Intrinsic term)의 선택성만이 일치하였고 $OH^-$의 경우에는 두 항중 어느것도 실험결과로 얻은 선택성과 일치하지 않았다. 정류점에서 모든 종에 대한 MNDO최적화된 구조들을 밝혔다.

• 대한화학회지
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• 제27권1호
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• pp.1-8
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• 1983

단일양성자성용매(메탄올, 에탄올, 1-프로판올)와 단일반양성자성용매(아세톤, 아세토니트릴, 아세토페논, 니트로벤젠) 및 이성분혼합용매계(메탄올-아세톤, 메탄올-아세토니트릴, 메탄올-벤젠)에서 염화나프탈렌술포닐과 피리딘의 친핵성치환반응에 미치는 용매효과를 전기전도도법으로 연구하였다. 단일양성자성용매의 반응속도상수는 유전상수가 큰 쪽에서 크게 관측되었고 반양성자성 용매의 반응속도상수는 유전상수가 큰 쪽에서 작게 나타났다. 아세토니트릴은 유전상수가 큰 반양성자성용매인데도 다른 반양성자성용매들보다 속도상수가 크게 관측되었다. 본 친핵성치환반응에서 용매효과는 ${\pi}^{\ast}$가 중요하고 염소이온의 이탈효과보다 수소결합형성이 전이상태를 안정화시키는데 기여함을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제15권2호
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• pp.161-167
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• 1994

Rate constants have been measured spectrophotometrically for the nucleophilic substitution reactions of aryl substituted benzenesulfonates (3) with alkali metal ethoxides ($EtO^-M^+$) and butane-2,3-dione monoximates ($Ox^-M^+$) in ethanol at $25^{\circ}C$. The reactivity of the alkali metal ethoxides decreases in the order $EtO^-K^+> EtO^- > EtO^-Li^+$, indicating that $K^+$ ion behaves as a catalyst and $Li^+$ ion acts as an inhibitor for all the substrates studied. For the corresponding reactions of 3 with Ox^-M^+$, $Li^+$ ion also exhibits inhibitory effect for all the substrates, while, $K^+$ ion shows catalytic or inhibitory effects depending on the nature of substituents on the acyl and phenyl moieties. A study of substituent effect on rate has revealed that both EtO^- $and Ox^-$ systems have the same reaction mechanism. The different behavior shown by $K^+$ ion for the reaction of 3 with $EtO^-$ and $Ox^-$ would be attributed to a difference in charge polarization of S=O bond in the transition state between the two systems and/or a change in conformation of Ox^-K^+$.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2483-2487
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• 2010

Pseudo-first-order rate constants ($k_{obsd}$) were measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl picolinate (6) with alkali metal ethoxides (EtOM, $M^+\;=\;K^+$, $Na^+$ and $Li^+$) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plot of $k_{obsd}$ vs. [EtOM] exhibits upward curvature regardless of the nature of $M^+$ ions. However, the plot for the reaction of 6 with EtOK is linear with significantly decreased $k_{obsd}$ values when 18-crown-6-ether (18C6, a complexing agent for $K^+$ ion) is added in the reaction medium. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constant for the reaction with dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that ion-paired EtOM is 3~17 times more reactive than dissociated $EtO^-$. The reaction has been proposed to proceed through a 5-membered cyclic transition state, in which $M^+$ ion increases the electrophilicity of the reaction site. Interestingly, $Na^+$ ion exhibits the largest catalytic effect. The presence of a nitrogen atom in the pyridine moiety of 6 has been suggested to be responsible for the high $Na^+$ ion selectivity.

• 한국식품영양학회지
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• 제5권1호
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• pp.23-32
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• 1992

Kinetic studies of nucleophilic substitution reactions of dansyl, bansyl, dabsyl chlorides with pyridines have been investigated at $0^{\circ}C$ in a range of methanol-acetonitrile binary solvent mixtures. The order of magnitude for reactivity of substrates with pyridines in the same reaction condition is dabsyl chloride>dansyl chloride> bansyl chloride. The value of $\rho$n(-2.29~ -4.66) and $\beta$(0.537~0.901) associated with a change substituent in the nucleophile are large and indicate a relatively advanced bond formation in the transition state. Solvatochromic correlations were predicted the increase of bond formation transition state according to the increasing MeCN contents, showing the greater contribution of polarity polarizability ($\pi$*) than hydro-gen bond donar acidity($\alpha$). We conclude that the reactions of dansyl, bansyl, dabsyl chlorides with pyridines proceed via associative Sn2 type reaction mechanism.

• Bulletin of the Korean Chemical Society
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• 제19권5호
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• pp.561-564
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• 1998

Solvent effects on the reactions of DANSYL and BANSYL chlorides with substituted pyridines have been investigated using two parameters of Taft's solvatochromic correlation and four parameters of Kirkwood-Onsager, Parker, Marcus, Hildebrand equation. The acetonitrile molecules accelerate charge separation of the reactants and stabilize the transition state. The coefficient of the solvent parameters provide a good information to predict and to analyze the reaction mechanism. The nucleophilic substitution reaction of DANSYL and BANSYL chlorides with substituted pyridines are ruled by the contribution of the change in dipole moment term and polarity-polarizability term.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1506-1510
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• 2014

A kinetic study on nucleophilic substitution reaction of 5-nitro-8-quinolyl picolinate (6) with alkali-metal ethoxides (EtOM; M = K, Na, and Li) in anhydrous ethanol is reported. The plot of $k_{obsd}$ vs. [EtOM] curves upward in the absence of crown ethers but is linear with significantly decreased reactivity in the presence of crown ethers. Dissection of $k_{obsd}$ into $k_{EtO}$- and $k_{EtOM}$ (i.e., the second-order rate constants for the reactions with the dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that the ion-paired EtOM is significantly more reactive than the dissociated $EtO^-$ (e.g., $k_{EtOM}/k_{EtO^-}$ = 33.4-141). This indicates that the reaction of 6 is catalyzed by $M^+$ ions in the order $Na^+$ > $Li^+$ > $K^+$ and the catalytic effect disappears in the presence of a proper crown ether. Picolinate ester 6 is much more reactive and is more strongly catalyzed by $M^+$ ions than 5-nitro-8-quinolyl benzoate (5). It has been concluded that $M^+$ ions catalyze the reaction of 6 by increasing electrophilicity of the reaction center through a cyclic transition state, which is structurally not possible for the reaction of 5.

• Bulletin of the Korean Chemical Society
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• 제23권9호
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• pp.1263-1307
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• 2002

Pseudo-first-order rate constants (kobs) have been determined for the nucleophilic substitution reactions of p-nitrophenyl diphenyl phosphinate (PNPDPP) with substituted phenoxides (XC6H4O - ) and butane-2,3-dione monoximate (Ox- ) in 0.1 M borate buffer (pH = 10.0) at 25.0 ${\pm}0.1^{\circ}C$. The kobs value increases sharply upon addition of cethyltrimethylammonium bromide (CTAB) to the reaction medium up to near 7 ${\times}$ 10-4 M CTAB and then decreases smoothly upon further addition of CTAB. The rate enhancement upon the addition of CTAB is most significant for the reaction with -O2CC6H4O- and least significant for the one with C6H5O- , indicating that the reactivity of these aryloxides in the presence of CTAB cannot be determined by the basicity alone. The strength of the interaction of these anionic aryloxides with the positively charged micellar aggregates has been suggested to be an important factor to determine the reactivity in the presence of CTAB. The kobs value for the reaction with Ox- increases also upon the addition of CTAB. However, the increase in the kobs value is much more significant for the reaction with Ox- than for the one with ClC6H4O- , indicating that Ox- is less strongly solvated than ClC6H4O- in H2O. The ${\alpha}-effect$ shown by Ox- in H2O has been attributed to the ground-state solvation difference between Ox- and ClC6H4O- .

• 대한화학회지
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• 제22권6호
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• pp.396-402
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• 1978

N-아세틸피페리돈과 그 양성자 첨가물의 형태 및 산-촉매 친핵성 치환반응에 대하여 EHT 및 CNDO/2 MO법과 궤도함수 혼합법을 적용하여 연구하였다. 계산 결과는 분자의 형태가 half-chair, cis-trans형이 가장 안정하며 양성자화는 아세틸카르보닐 산소에서 더 용이하게 일어남을 나타내고 있다. 이 결과를 콘쥬게이션, 정전기적 및 입체효과로서 설명하였다. 그리고 전하-조절 반응에서는 카르보닐 탄소원자의 양전하의 증가가, 궤도함수 조절반응에서는 LUMO AO 계수의 증가가 양성자화된 카르보닐 탄소의 반응성을 크게 증가시켜 친핵성 치환반응에서는 아세틸 절단이 개환반응보다 용이함을 밝혔다.