• Title, Summary, Keyword: substituent effect

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Substituent Effect in Photochemistry of Carbonyl Compounds: α-Halovalerophenones

  • Cho, Sung-Su;Park, Bong-Ser
    • Bulletin of the Korean Chemical Society
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    • v.25 no.1
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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.

Effect of Substituents on Benzenesulfonyl Motif of 4-Phenyl-1-arylsulfonylimidazolidinones for Their Cytotoxicity

  • Lee, Hui-Soon;Park, Kyung-Lae;Choi, Sang-Un;Lee, Chong-Ock;Jung, Sang-Hun
    • Archives of Pharmacal Research
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    • v.23 no.6
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    • pp.579-584
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    • 2000
  • To explore the effect of substituents' on phenyl motif on sulfonyl function of novel anticancer 4-phenyl-1-benzenesulfonylimidazolidinones (1), electron donating or withdrawing sub-stituents were introduced at 3 or 4-position and the analogs were tested against human lung (A549) and colon (HCT-15) cancer cell lines. Quantitative structure activity relation-ship of the 4-substituted series shows that only STERIMOL L values are well correlated. The increment of substituent's volume enhances the activity against both cell lines. The small substituent at 3-position additionally increases the activity. However naphthyl group in place of phenyl reduces the activity, Therefore the phenyl motif with sterically large substituent at 4-position and small substituent at 3-position may be important for their activity. Integration of these substituents' effects into the structural design led to discover the more potent analog, 4-phenyl-1-(N-acetylindoline-5-sulfonyl) imidazolidinone (1n).

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Correlation of Chemical Shifts with Substituent Parameters in N-Benzyl Derivatives of Pyrrole,3a,7a-Dihydroindole,and Indole Esters

  • Jeon, Kyu-Ok;Yu, Sook-Yu;Lee, Chang-Kiu
    • Bulletin of the Korean Chemical Society
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    • v.23 no.9
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    • pp.1241-1255
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    • 2002
  • Series of m- and p-substituted benzyl derivatives of pyrrole, tetramethyl 1-benzyl-3a,7a-dihydroindole-2,3,3a,4-tetracarboxylate, and trimethyl 1-benzylindole-2,3,4-tricarboxylate were prepared and their 13C NMR spectra were obtained in 0.1 M solutions of chloroform-d. Both single substituent parameter and dual substituent parameter analyses were carried out to correlate the substituent chemical shifts. The ${\beta}$ carbon of the indole series showed the most profound substituent effect dependence as well as the best correlation. The results are explained by the hyperconjugation of the benzyl methylene group.

Semiempirical Calculations of Substituent Effects on the Reactions of Cephem-Like β-Lactam Molecules

  • 이정철;고헌영;창문호;이윤섭
    • Bulletin of the Korean Chemical Society
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    • v.17 no.7
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    • pp.604-607
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    • 1996
  • Semiempirical PM3 MO calculations are applied to estimate both 1-atom (X=S,O,C) and 3-substituent (Y=R, CH2R, SR, CH2SR) effects on the reactions of some 1-atom-replaced and 3-substituted cephem-like β-lactam compounds of thiacephems, oxacephems, and carbacephems. Stabilization energy (SE) of the reaction intermediate for the reaction with a hydroxyl ion can be used to evaluate the facility of a reaction and selected as a chemical reactivity index. With the 1-atom effect only, the SE values obtained imply that thiacephems are generally more reactive than the other two cephem-like molecules and the reactivity order is thiacephems>oxacephems>carbacephems. When it comes to the 3-substituent (Y=R, CH2R, SR, CH2SR) effect, chemical reactivity can be best realized by using a 3-substituted thiacephem molecule capable of giving a resonance-stabilized and electron-rich leaving group after the reaction with a nucleophile. SE values, however, decrease in most cases when an additional intervening ethylene group is present (Y=CH2R, CH2SR). The overall 3-substituent reactivity tendency is SR>CH2SR>R>CH2R.

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Substituent Effect on Diastereoselectivity in Photochemistry of Valerophenone

  • Park, Bong-Ser;Cho, Sung-Su;Chong, Sang-Hyuk
    • Bulletin of the Korean Chemical Society
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    • v.28 no.7
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    • pp.1156-1158
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    • 2007
  • Valerophenone shows a dramatic shift of photoreactivity by a cyclopropyl group at alpha position to the carbonyl group. By the minor change of structure, the diastereoselectivity of the Yang photocyclization is reversed and the ratio of cyclization to elimination products increases significantly.

The Salt Effect on the Nucleophilic Substitution Reaction

  • Hee Hyun Park;Young Seok Hong;Dae-Dong Sung
    • Bulletin of the Korean Chemical Society
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    • v.12 no.3
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    • pp.295-301
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    • 1991
  • The nucleophilic substitution reactions of p-substituted benzenesulfonyl chlorides wiht p-substituted anilines were carried out in 1,1,1,3,3,3-hexafluoro-2-propanol and 2-propanol mixtures. The salt effect was observed to be inhibited by the reaction of 1,1,1,3,3,3-hexafluoro-2-propanol with nucleophiles. To investigate the effectiveness of the salt for the nucleophilic substitution reaction the relative salt effect was determined. According to the comparison with the inhibitive salt effect and the substituent effects for the substrates and nucleophiles, the reactions were predicted to be controlled by the salt effect more than substituent effect in HFP-PrOH mixtures.

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Determination of Reactivity by MO Theory (Part 32). MO Studies of Substituent Effects on the Gas-Phase Decarboxylation of But-3-enoic Acid (분자궤도론에 의한 반응성 결정 (제32보). 3-부테노산의 기체상 탈탄산반응에 미치는 치환기 효과의 분자궤도론적 연구)

  • Jeoung Ki Cho;Ikchoon Lee;Hyuck Keun Oh;In Ho Cho
    • Journal of the Korean Chemical Society
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    • v.28 no.5
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    • pp.279-283
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    • 1984
  • ${\beta}$-Substituent effect on the reactivity of retro-ene decarboxylation of but-3-enoic acid was investigated theoretically. It was found that charge effect is important not only through ${\pi}$-electron transfer as has been claimed to rationalize experimental results but also through polarization as found for the $CH_3$ substituent. The reactivity was not determined by the charge effect alone but the HOMO-LUMO energy gap was also found to affect the reactivity. In general it was confirmed that the greater the ${\pi}$-electron donating power of the substituent, the greater is the reactivity.

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Dual Substituent Effects on Anilinolysis of Bis(aryl) Chlorothiophosphates

  • Barai, Hasi Rani;Lee, Hai Whang
    • Bulletin of the Korean Chemical Society
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    • v.34 no.12
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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.

Alkyl and Alkenyl Substituent Effects on Nonbonded Interactions of Hexatriene

  • Lee, Ik-Choon;Rhyu, Keun-Bae;Lee, Bon-Su
    • Bulletin of the Korean Chemical Society
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    • v.2 no.1
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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.

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