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Keum, Sam-Rok,Ma, So-Young,Lim, Hyun-Woo,Han, Tae-Hwi,Choi, Kyu-Hyun Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.8
The position of the thermodynamic equilibrium for reverse thermochromic spiropyran 6-carboxylates (SP-COOHs) was easily determined in aqueous binary mixtures, such as water-methanol, water-acetonitrile and water-dimethyl sulfoxide. The existence of more than one type of interconvertible species of the ring-opened form of SP-COOH in aqueous binary solvents enables us to evaluate the molar extinction coefficients of the ring-opened species of SP-COOH and to obtain the thermodynamic parameters.
Dioxygen Transfer from 4a-Hydroperoxyflavin Anion to Isomeric Aminophenolates
Sam-Rok Keum,Ki-Bong Lee,Thomas C. Bruice Korean Chemical Society 1990 Bulletin of the Korean Chemical Society Vol.11 No.2
The dioxygen transfer reaction from $N^5$-ethyl-4a-hydroperoxy-3-methyllumiflavin anion (4a-FlEtOO-) has been extended to isomeric aminophenol systems (1a-4a). O-aminophenol (o-AP, 1a & 2a) and p-aminophenol(p-AP, 3a & 4a) were turned out to be good substrates, whereas m-aminophenol(m-AP, 5a) was not. This is due to the charge location which is not on the carbon bearing the amino group. o-AO's react with 4a-FlEtOO- to give isophenoxazine derivatives (6 & 7) and with p-AP's to produce p-benzoquinone derivatives (8 & 9). The partition coefficients $(k_2/k_3)$ of 1a & 2a were $4.84{\times}10^{-4}\;&\;1.66{\times}10^{-5}M$, respectively and those of methylated aminophenolates, 2a & 4a were 4-10 times greater than nonmethylated substrates, 1a & 3a.
Keum, Sam-Rok,Ku, Byung-Soo,Kim, Sang-Eun,Choi, Yoon-Ki,Kim, Sung-Hoon,Koh, Kwang-Nak Korean Chemical Society 2004 Bulletin of the Korean Chemical Society Vol.25 No.9
Solvatokinetic and solvatochromic behavior of bis(indolinobenzospiropyranyl) sulfide derivatives 1a-1c have been studied in various solvents. The marked negative solvatochromism is exhibited for 1a and 1b in the whole region of solvent polarity examined. Whereas, it is found only in the polar solvent region ($E_T$ > 37) for 1c. The sensitivity order to the solvent media (slope values) is 1a > 1b > 1c. The branched linear plot with a zero slope was shown for the most sterically-hindered compound 1c in the less polar-solvent region (($E_T$ < 37). The biphasic plot is indicative of dual mechanistic process, i.e., a transition state with increased zwitter-ionic character in more polar solvents and electrocyclic process with an isopolar transition state in less polar solvents.
Keum, Sam-Rok,Roh, Se-Jung,Kim, Young-Nan,Im, Do-Hyuck,Ma, So-Young Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.11
The unequivocal solid-state structure and stereochemistry of the hetaryl leuco-TAM dye, 2,2’-(2-phenyl propane- 1,3-diylidene) bis(1,3,3- trimethylindoline) derivatives were established using X-ray single crystal analysis. The X-ray crystal analysis showed that the (Z, E)-isomers only formed stereoselectively, with a so-called “threebladed propeller” conformation, from the reaction of a Fischer base and benzaldehyde derivatives. These isomers were stacked in a juxtaposition to form a dimer or a double dimer, adopting either a triclinic, with P-1, or monoclinic crystal system with a space group P21/n in the unit cell of the crystal.
Buncel, Erwin,Keum, Sam-Rok,Rajagopal, Srinivasan,Cox, Robin A. Canadian Science Publishing 2009 Canadian journal of chemistry Vol.87 No.8
<P> Kinetic studies of the Wallach rearrangements of four azoxypyridines, four azoxypyridine N-oxides, and one azoxypyridine N-methiodide have been carried out in the 100% H2SO4 acidity region. For all of the β-isomers in the study the reactions proceeded at a spectrally measurable rate, and the log observed rate constants were found to be linear functions of the log H3SO4<SUP>+ </SUP> concentration, as previously found for azoxybenzene itself, suggesting that the reaction mechanism for these substrates is the same as that previously deduced for axozybenzene, i.e., a general-acid-catalysis A-SE2 process. For the α-azoxypyridines no reaction could be observed at all. The two α-azoxypyridine N-oxides in the study did react, albeit very slowly, but for these two compounds the log observed rate constants were not linear functions of the log H3SO4<SUP>+ </SUP>concentration, but were instead found to be linear in the H0 acidity function, which is known for the 100% H2SO4 acidity region. It follows that the reaction mechanism for these α-isomers is a different one, presumably an A1 process. This mechanism was proposed back in 1963 for azoxybenzene, but has never actually been observed for any substrate before the work reported in this study. Thus, the Wallach rearrangement story can be said to have come full circle. </P>