• Bulletin of the Korean Chemical Society
• /
• 제25권1호
• /
• pp.42-44
• /
• 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
• /
• 제23권9호
• /
• pp.1241-1255
• /
• 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.

• Archives of Pharmacal Research
• /
• 제23권6호
• /
• pp.579-584
• /
• 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).

• Bulletin of the Korean Chemical Society
• /
• 제2권1호
• /
• pp.12-16
• /
• 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
• /
• 제17권9호
• /
• pp.831-835
• /
• 1996

New dynemicin A mimics with methyl group 2a and 2b were synthesized, and acid-induced hydrolyzed to see an electronic effect of substituent for epoxide opening. The model 2a with methyl group at C3 position was more rapidly transformed to diol 16a than 2b with methyl group at C2. This result suggests that any substituent at C3 position plays more important role than any substituent at C2 position in the dynemicin A mimic activation.

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

• 대한화학회지
• /
• 제28권5호
• /
• pp.279-283
• /
• 1984

but-3-enoic acid의 retro-ene 탈탄산 반응에 있어서 그 반응성에 대한 ${\beta}$-치환기 효과를 이론적으로 연구하였다. 그 결과 전하 효과에서, 실험에서의 치환체에 의한 ${\pi}$-전자 전달만이 관여되는 것이 아니라, $CH_3$-치환같은 경우는 편극 효과도 상당히 관여됨을 알 수 있었다. 그러나 이들 반응성을 전하 효과로만 결정지을 수 없으며, HOMO와 LUMO간의 에너지 간격이 또한 반응성에 크게 영향을 미친다. 결과적으로, 일반적으로 논하는 치환체의 ${\pi}$-전자 주게 능력이 클수록 반응이 빨라진다는 사실에는 변함이 없었다.

• Bulletin of the Korean Chemical Society
• /
• 제35권3호
• /
• pp.737-742
• /
• 2014

The vibronic emission spectra of isomeric trimethylbenzyl radicals were reassigned based on substituent effect on electronic transition energy as well as ab initio calculation of the benzyl radical. The electronic transition energy of three isomeric jet-cooled trimethylbenzyl radicals produced by corona discharge of 1,2,3,5-tetramethylbenzene were analyzed using the empirical data of three isomeric methylbenzyl radicals. Calculated data were obtained by summing up the shifts measured from methylbenzyl radicals as well as taking the position and alignment of substituents on the benzene ring into account. The revised assignments show better agreement with observation, and rationalize the validity of the model developed to explain the substituent effect on electronic transition energy of benzyl radicals.

• Bulletin of the Korean Chemical Society
• /
• 제17권8호
• /
• pp.693-695
• /
• 1996

The steric effect on the first order hyperpolarizability of the β-nitrostyrene derivatives has been investigated by comparing the β values and the dihedral angles between the aryl and nitroalkenyl groups. In general the β value increased with the electron-donating ability of the substituent. The larger β value for 3,4-dimethoxy-β-nitrostyrene than that for p-methoxy-β-nitrostyrene has been attributed to the lower charge transfer energy for the former. The most striking substituent effect was observed in the β-methyl-β-nitrostyrene derivatives. Thus the β values for 3,4-dimethoxy- and p-methoxy derivatives of the latter decreased to near zero, probably because of the large distortion from planarity caused by the steric repulsion between the β-methyl and the aryl groups. The larger β value for p-dimethylamino-β-methyl-β-nitrostyrene has been interpreted with an increased electron-donating ability of the substituent and increased co-planarity.

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