• Title/Summary/Keyword: Substituents

Search Result 568, Processing Time 0.03 seconds

Electrochemical Reduction of Nitrobenzene and Substituted Nitrobenzenes on Lead Electrode

  • Chon, Jung-Kyoon;Paik, Woon-Kie
    • Bulletin of the Korean Chemical Society
    • /
    • v.2 no.1
    • /
    • pp.1-8
    • /
    • 1981
  • Electrochemical reduction of nitrobenzene and substituted nitrobenzenes on lead electrode was studied by galvano-static measurements and cyclic voltammetry in basic ethanol-water solvents. Nitroso compounds or hydroxylamines were detected as the main reduction product depending on the potential. Mechanisms of production and further reduction of substituted and unsubstituted nitrosobenzenes are deduced from Tafel slope, pH dependence and reaction order. The reduction of most of the substituted nitrobenzenes to corresponding nitrosobenzene derivatives seemed to follow the reaction mechanism of nitrobenzene reduction with a few exceptions. A Hammett type relationship between the magnitude of the reduction current and the kinds of substituents was found with the ${\rho}$ value of 0.54.

Synthesis and Properties of Thermotropic Compounds with Two Terminal Mesogenic Units and a Central Spacer (Ⅵ). Homologous Series of $\alpha,\;\omega$-Bis[4-(p-substituted benzoyloxy)benzoyloxy]alkanes$^*$

  • Jin, Jung-Il;Seong, Churl-Min;Jo Byung-Wook
    • Bulletin of the Korean Chemical Society
    • /
    • v.6 no.1
    • /
    • pp.40-45
    • /
    • 1985
  • The thermal and optical properties of two new series of thermotropic, liquid crystalline compounds were studied by differential scanning calorimetry and on the hot-stage of a polarizing microscope. The first series contained two identical mesogenic units, 4-(p-phenylbenzoyloxy) benzoate moieties, at both ends of the polymethylene spacer of varying lengths and the second series, mesogenic units with different substituents and the hexamethylene group as the central spacer. A thermodynamic analysis of the phase transitions of the compounds was made and the results were discussed in relation to their chemical structures.

Basicity of Urea: Near-Infrared Spectroscopic and Theoretical Studies on the Hydrogen Bonding Ability of TMU and DMDPU

  • 이호진;최영상;박정희;윤창주
    • Bulletin of the Korean Chemical Society
    • /
    • v.19 no.1
    • /
    • pp.110-114
    • /
    • 1998
  • The hydrogen-bonding interactions between thioacetamide (TA) and urea derivatives such as tetramethylurea (TMU) and dimethyldiphenylurea (DMDPU) have been studied using near-infrared absorption spectroscopy. Thermodynamic parameters for the interactions between TA and urea derivatives were determined by analyzing the $v^{as}_{N-H}$+Amide Ⅱ combination band of TA at 1970 nm. The ΔH° values, indicating the intrinsic strength of hydrogen bonding, are - 23.0 kJ/mole and - 19.8 kJ/mol for TMU and DMDPU, respectively. This is well explained by the inductive effects of substituents. Ab initio molecular orbital calculations for the proton affinity of TMU, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) in gas phase have been carried out at HF/3-21G ad HF/6-31G(d) levels, showing that the proton affinity of TMU is larger than that of DMA, which agrees well the experimental results.

Cross Interaction Constants As a Measure of the Transition State Structure (Part 2). Nucleophilic Substitution Reactions of Phenacyl Bromides with Aniline in Methanol-Acetonitrile Mixtures

  • Lee, Ik-Choon;Kim, In-Chul
    • Bulletin of the Korean Chemical Society
    • /
    • v.9 no.3
    • /
    • pp.133-135
    • /
    • 1988
  • Kinetics and mechanism of the nucleophilic substitution reactions of phenacyl bromides with anilines in methanol-acetonitrile mixtures at $45.0^{\circ}C$ are reported. The reaction is found to proceed via $S_N2$ process, but the magnitudes of cross interaction constants, ${\rho}_{XY}$, between substituents X in the nucleophile and Y in substrate were unusually small, even after allowing for the fall off due to non-conjugative intervening -CO group in the reactant. As in the other phenacyl derivatives, the resonance shunt phenomenon was invoked to explain the remarkable diminuation of the $|{\rho}_{XY}|$ values.

A Structure-Based Activation Model of Phenol-Receptor Protein Interactions

  • 이경희
    • Bulletin of the Korean Chemical Society
    • /
    • v.18 no.1
    • /
    • pp.18-23
    • /
    • 1997
  • Data from structure/activity studies in vir gene induction system have led to evaluate the working hypothesis of interaction between phenolic inducers and phenol binding proteins. The primary specificity in the association of a phenolic inducer with its receptor in our system is hypothesized to be the hydrogen bonding interactions through the ortho methoxy substituents as well as the proton transfer between the inducer and the binding protein. In this paper the proposed working model for phenol-mediating signal transduction was evaluated in several ways. The importance of the general acid-base catalysis was first addressed by the presence of an acidic residue and a basic residue in the phenol binding protein. Series of compounds were tested for vir gene expression activity to confirm the generation of a strong nucleophile by an acidic residue and an involvement of a basic residue as a proton acceptor. An attempt was made to correlate the pKa values of the phenolic compounds with vir gene induction activities as inducers to further support the proposed proton transfer mechanism. Finally, it was also observed that the regioselectively attached methoxy group on phenol compounds is required as the proper hydrogen bond acceptor.

Studies on the Linear Free Energy Relationship in Methyl Cinnamates by $^1$H-NMR Spectrometry

  • Shim, Sang-Chul;Park, Joon-Won
    • Bulletin of the Korean Chemical Society
    • /
    • v.2 no.1
    • /
    • pp.29-34
    • /
    • 1981
  • Chemical shift values of ${\alpha}$-proton of trans- and cis-methyl cinnamates are well correlated with ${\sigma}({\sigma}_1,\; {{\sigma}_R}^{\alpha})$, and (F, R) (r=0.999-0.879). It is observed that (1) the degree of variation of ${\delta}H_{\alpha}$ value by varying the substituents in trans-cinnamates is similar to that of cis-cinnamates $({\rho}_{trans}=0.296,\;{\rho}_{cis}=0.2840, (2) resonance contribution is larger in the trans-cinnamates than that in the cis-cinnamates, but inductive contribution is reversed, (3) for m-substitued derivatives, resonance contribution is very small compared to that for p-substituted derivatives.

Direct Synthesis of ${\eta}^6$-1-Functionally Substituted 2,3,4,5-Tetraphenyl-1-Silacyclopentadiene Complexes of Chromium

  • Wan-Chul Joo;Jang-Hwan Hong;Hong Lae Sohn;Eun-Kyoung Kang;Chang-Hwan Kim
    • Bulletin of the Korean Chemical Society
    • /
    • v.11 no.1
    • /
    • pp.31-33
    • /
    • 1990
  • We synthesized the novel complexes of (1,1-dimethyl-3,4-diphenyl-1-silacyclopenta-2,4-di ene-2,5-yldibenzene)bis(tricarbonylchromium) and tricarbonyl (R,R'-3,4,5-triphenyl-1-silacyclopenta-2,4-diene-2 -ylbenzene)chromium(R,R' = Me, R = Me/R' = Cl, R = Ph/R' = Cl) from the reaction of the corresponding R,R'-2,3,4,5-Tetraphenyl-1-silacyclopenta-2,4-dien e (abr. R,R'-TPSCp) with chromiumhexacarbonyl. These results reveal that chromium prefer to coordinate to the phenyl substituents of 1-silacyclospentadiene rather than the butadiene moiety of the ring.

Solvolyses of N-Methyl-N-phenylcarbamoyl Chlorides with Electron Acceptor Substituents in A Queous Binary Mixtures

  • Gu, In Seon;An, Seon Gyeong;Yang, Yeol;Go, Han Jung;Choe, Mun Ho;Lee, Ik Chun
    • Bulletin of the Korean Chemical Society
    • /
    • v.22 no.8
    • /
    • pp.842-846
    • /
    • 2001
  • Solvolyses of N-methyl-N-phenylcarbamoyl chlorides in aqueous binary mixtures of acetone, ethanol, methanol and in water, D2O, and 50% D2O-CH3OD are investigated at 25.0 $^{\circ}C.$ The Grunwald-Winstein plots of first-ord er rate constants for N-methyl-N-phenylcarbamoyl chlorides with YCl (based on 2-adamantyl chloride) show a dispersion phenomenon. The ring parameter (I) has been shown to give considerable improvement when it is added as an hI term to the original Grunwald-Winstein and extended Grunwald-Winstein correlations for the solvolyses of N-methyl-N-phenylcarbamoyl chlorides. This study has shown that the magnitude of l, m and h values associated with a change of solvent composition is able to predict the dissociative SN2 transition state. The kinetic solvent isotope effects determined in deuterated water are consistent with the proposed mechanism of the general base catalyzed and/or a dissociative SN2 mechanism channel for N-methyl-N-phenylcarbamoyl chlorides solvolyses.

Semiempirical Molecular Orbital Calculations of the Substituent Effects on Acylations of 3-Cephem Analogues

  • Chang Moon-Ho;Koh Hun-Yeong;Lee Jung-Chull;Lee Yoon Sup
    • Bulletin of the Korean Chemical Society
    • /
    • v.15 no.6
    • /
    • pp.453-455
    • /
    • 1994
  • Semiempirical MO calculations are applied to estimate the substituent effects on acylations of the nonfused N-vinyl-2-amino $\beta-lactams$ having frameworks analogous to 3-cephems. The stabilization energy for the reaction intermediate of the nucleophilic attack by the hydroxide ion is selected as the reactivity index and calculated by AM1 and PM3 methods for the model $\beta-lactams$ with substituents at the C1 and N-vinyl terminal positions. The reactivities are larger for -SH connected to the C1 and strong $\pi-acceptors$ at the N-vinyl terminal implying the large reactivity for known active cephalosporins. Quantum chemical calculation of stabilization energy could be useful in correlating antibiotic activities of many compounds obtained as derivatives of a lead compound.

Theoretical Studies on Phentl Group Migration of Protonated 1,2-Diphenyl Hydrazines

  • Kim, Chan Gyeong;Lee, In Yeong;Kim, Jang Geun;Lee, Ik Chun
    • Bulletin of the Korean Chemical Society
    • /
    • v.21 no.5
    • /
    • pp.477-482
    • /
    • 2000
  • Phenyl group migration within protonated 1,2-diphenyl hydrazines has been studied theoretically using the semi-empirical AM1 method. This reaction proceeds through a 3-membered cyclic transition state and requires high activation energy. In the reactant, there was no resonance stabilization for the moving Z-ring, however, hammett $p_Z^+$ values are large due to the direct involvement of the Z-ring inthe reaction, and the development of a negative charge on the reaction center gives them a posifive value. In the case of the non-moving ring, $p_Y^+$ values are small and negative owing to the smaller positive charge increase in the reaction center. The cross-interaction constant, $p_YZ^+$, was obtained from the activation enthalpies, using the multipe linear regression methdo, and the interaction between two substituents, Y and Z, is examined.