• Bulletin of the Korean Chemical Society
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• 제25권1호
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• pp.42-44
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• 2004

Valerophenones containing a substituent at alpha position to the carbonyl group show the remarkable substituent effects on their photochemical reactions. ${\alpha}$-Bromovalerophenone gives only the C-Br bond cleavage products, but the ${\alpha}$-chlorovalerophenone follows the classical Norrish/Yang reaction pathway predominantly.

• Bulletin of the Korean Chemical Society
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• 제28권6호
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• pp.1031-1034
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• 2007

The R- and Z-substituent effects for the gas-phase thermal decompositions of carbamates, R2NC(=O)- OCH2CH2Z, have been investigated theoretically at B3LYP level with 6-31G(d) and 6-31++G(d,p) basis sets. Both the Z- and R-substituent effects on reactivity (ΔH≠) were well consistent with experimental results, although the R-substituent effect was underestimated theoretically. No correlations were found between activation enthalpies and reaction enthalpies. The substituent effects on reactivity seemed to be complicated at a glance, but were understandable by concurrent electronic and steric factors. Variations of bond lengths at TS structures were well correlated with the Taft's σ* values and the TS structures became tighter as the Zsubstituent became a stronger electron-acceptor (δσ* > 0). However the effects of R-substituents on the TS structures were much smaller when compared to those of Z-substituents.

• 대한화학회지
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• 제19권2호
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• pp.116-122
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• 1975

Benzyl arenesulfonate와 피리딘과의 아세톤 용매중에서의 反應速度를 測定하였다. Benzyl arenesulfonate의 離脫基의 치환기효과는 p-MeO基 및 $p-NO_2$기를 除外하고는 Hammett 式에 잘 적용되었으며, 전자끄는기는 반응속도를 증가시켰다. 離脫基의 치환효과는 벤질炭素에 아민이 親核的으로 공격하여 전이상태에서 치환기의 電子끄는 능력이 C-N 結合의 形成과 C-O結合의 쪼개짐에 변화를 주고 있다는 사실로서도 설명이 되어진다. 치환기효과는 benzyl p-bromobenzeneslfonate가 benzyl p-nitrobenzenesulfonate보다 N-C結合이 tight 한 전이상태의 구조를 가지고 있음을 말해주며 이는 結合의 형성과 쪼개짐에 있어 Thornton의 $S_N2$전이상태 구조의 예상과도 잘 符合된다.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1460-1464
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• 2014

The substituent effects on the pyridinolysis (XC5H4N) of Y-aryl ethyl chlorophosphates are investigated in acetonitrile at $35.0^{\circ}C$. The two strong ${\pi}$-acceptor substituents, X = 4-Ac and 4-CN in the X-pyridines, exhibit large positive deviations from the Hammett plots but little positive deviations from the Br$\ddot{o}$nsted plots. The substituent Y effects on the rates are really significant and the Hammett plots for substituent Y variations in the substrates invariably change from biphasic concave downwards via isokinetic at X = H to biphasic concave upwards with a break point at Y = 3-Me as the pyridine becomes less basic. These are interpreted to indicate a mechanistic change at the break point from a stepwise mechanism with a rate-limiting bond formation (${\rho}_{XY}$ = -6.26) for Y = (4-MeO, 4-Me, 3-Me) to with a rate-limiting leaving group expulsion from the intermediate (${\rho}_{XY}$ = +5.47) for Y = (4-Me, H, 3-MeO). The exceptionally large magnitudes of ${\rho}_{XY}$ values imply frontside nucleophilic attack transition state.

• 대한화학회지
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• 제44권3호
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• pp.184-189
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• 2000

메타-치환 피리딘의 치환기 효과를 조사하기 위하여 ab initio 계산을 수행하였다. 여러 메타-치환 피리딘의 최적화 된 구조로부터 정전기전위를 계산하였으며, 그 결과 피리딘의 질소 원자에서 최소정전기전위 값을 나타내었다. 최소정전기전위 값을 나타내었다. 최소정전기전위 값을 Hammett 치환기 상수, ${\sigma}_m$ 및 ${\Delta}pK_a$ 와 비교한 결과 흘륭한 상관성이 있음을 알았으며, 따라서 최소정전기전위가 치환기 효과를 나타내는 유용한 척도로 사용될 수 있음을 알 수 있었다.

• 대한화학회지
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• 제43권4호
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• pp.378-383
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• 1999

파라-치환 피리딘의 치환기 효과를 조사하기 위하여 Ab initio 계산을 수행하였다. 여러 치환 피리딘의 최적화 된 구조로부터 정전기전위를 계산한 결과 피리딘의 질소 원자에서 최소값을 나타내었으며, 최소정전기전위 값은 Hammett 치환기 상수, ${\sigma}_p$ 및 ${\Delta}pKa$와 홀륭한 상관성이 있음을 알았다. 그 결과 최소정전기전위가 치환기 효과를 나타내는 척도로 사용될 수 있음을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제2권1호
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• pp.12-16
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• 1981

Alkyl and alkenyl substituent effects on nonbonded interactions of hexatriene were examined using CNDO/2 method. The results showed that: (1) rapid rate of thermal electrocyclization of 3-vinyl hexa-1, 3, 5-triene is due to increased overlap population between atom pair reacting resulting from strong electron repelling interaction of vinly group on the triene moiety; (2) stability of a conformer is determined by additive effect of composite ${\pi}$ structures; (3) a substituent on positions 2 and 3 increases the HOMO AO coefficient of sites 1 and 4 considerably and activates interactions with these sites.

• Bulletin of the Korean Chemical Society
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• 제25권10호
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• pp.1463-1464
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• 2004

• Bulletin of the Korean Chemical Society
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• 제32권6호
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• pp.1939-1944
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• 2011

The nucleophilic substitution reactions of bis(Y-aryl) chlorophosphates (1) with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at 35.0 $^{\circ}C$. The kinetic results of 1 are compared with those of Y-aryl phenyl chlorophosphates (2). The substrate 1 has one more identical substituent Y compared to substrate 2. The cross-interaction between Y and Y, due to additional substituent Y, is significant enough to result in the change of the sign of cross-interaction constant (CIC) from negative ${\rho}_{XY}$ = -1.31 (2) to positive ${\rho}_{XY}$ = +1.91 (1), indicating the change of reaction mechanism from a concerted $S_N2$ (2) to a stepwise mechanism with a rate-limiting leaving group departure from the intermediate (1). The deuterium kinetic isotope effects (DKIEs) involving deuterated anilines ($XC_6H_4ND_2$) show secondary inverse, $k_H/k_D$ = 0.61-0.87. The DKIEs invariably increase as substituent X changes from electron-donating to electron-withdrawing, while invariably decrease as substituent Y changes from electron-donating to electron-withdrawing. A stepwise mechanism with a rate-limiting bond breaking involving a predominant backside attack is proposed on the basis of positive sign of ${\rho}_{XY}$ and secondary inverse DKIEs.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3597-3601
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• 2013

The reactions of bis(Y-aryl) chlorothiophosphates (1) with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at $55.0^{\circ}C$. The Hammett plots for substituent Y variations in the substrates show biphasic concave upwards with a break point at Y = H. The cross-interaction constants (${\rho}_{XY}$) are positive for both electron-donating and electron-withdrawing Y substituents. The kinetic results of 1 are compared with those of Y-aryl phenyl chlorothiophosphates (2). The cross-interaction between Y and Y, due to additional substituent Y, is significant enough to result in the change of the sign of ${\rho}_{XY}$ from negative with 2 to positive with 1. The effect of the cross-interaction between Y and Y on the rate changes from negative role with electron-donating Y substituents to positive role with electron-withdrawing Y substituents, resulting in biphasic concave upward free energy correlation with Y. A stepwise mechanism with a rate-limiting leaving group departure from the intermediate involving a predominant frontside attack hydrogen bonded, four-center-type transition state is proposed based on the positive sign of ${\rho}_{XY}$ and primary normal deuterium kinetic isotope effects.