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  • 1
    Digitale Medien
    Digitale Medien
    Formation of 9,10-diphenylanthracene radical cation from Friedel-Crafts alkylation reactions. Absence of the triphenylsilyl radical (1988)
    s.l. : American Chemical Society
    The @journal of organic chemistry 53 (1988), S. 698-700 
    Details
    ISSN: 1520-6904
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/jo00238a043
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  • 2
    Digitale Medien
    Digitale Medien
    Comment on: "Adiabatic processes in monatomic gases'' (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2526-2528 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The adiabatic processes at zero rate are reversible processes, while at a constant finite rate are irreversible. The formulation employing state variables to describe the irreversible process of nonequilibrium system and the illustration of the finite-rate model with a Carnot cycle are not valid. The intermediate nonequilibrium processes should be described through a state-variable-free approach.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.455948
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  • 3
    Digitale Medien
    Digitale Medien
    Coenzyme F430 from Methanogenic Bacteria: Mechanistic studies on the reductive cleavage of sulfonium ions catalyzed by F430 pentamethyl ester (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 1478-1490 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Mechanistic questions regarding the reductive cleavage of sulfonium ions by the NiI form of coenzyme F430 pentamethyl ester (F430M) were addressed in a series of kinetic studies and isotope labeling experiments. In neat DMF, methane formation from dialkyl(methyl)sulfonium ions consistently showed a delay time of ca. 1 h. In the presence of excess propanethiol, no delay was observed and methane formation followed pseudo-first-order kinetics with a logarithmic dependence of the initial rate on the concentration of propanethiol. From the temperature dependence of the reaction rate, an estimate for the activation parameters of ΔH# = 49 kJ mol-1 and (apparent) ΔS# = -114 J K-1 mol-1 was derived. The observation of deuterium incorporation into methane from (CH3)2CHOD, but not from (CH3)2CDOH, indicates that the fourth H-entity is introduced into CH4 as a proton, and that free CH3 radicals are not involved. In contrast to the reaction with the homogeneous one-electron reductant sodium naphthalide, the F430M-catalyzed reduction of mixed dialkyl(methyl)sulfonium ions showed a pronounced selectivity for the cleavage of Me—S over that of alkyl-S (alkyl ≠ Me) bonds. Mechanisms that are consistent with these results, as well as possible explanations for the time delay and the apparent highly negative entropy of activation, are discussed.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19920750504
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  • 4
    Digitale Medien
    Digitale Medien
    Synthesis of Spiro[cyclohexane-1,2′-[2H]indene] derivatives as inhibitors of steroid 5α-reductase (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 857-865 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The spiro[cyclohexane-1,2′-[2H]indene] derivatives 15a,b with molecular dimensions and nucleophilic functional groups similar to known steroid 5α-reductase inhibitors (e.g. 2) were synthesized. The spiro[cyclohexane-1,2′-[2H]indene]-1′(3′H),4-dione (5) was synthesized from 5-methoxyindan-l-one ( = 2,3-dihydro-5-methoxy-1H-inden-1-one). A Grignard reaction and a dehydration step led to the cyclohexene (±)-7 which, upon a stereoselective hydrogenation catalyzed by Raney-Ni under mild conditions, gave 8a as a pure epimer. Further hydrogenation and hydrogenolysis of 8a over Pd/C at room temperature reduced the keto group to give pure 9a. Finally, the 5′-substituted derivatives 12a, 14a, and 15a were generated by deprotection and Heck-type reaction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19950780407
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  • 5
    Digitale Medien
    Digitale Medien
    Coenzyme F430 from Methanogenic Bacteria: Detection of a Paramagnetic Methylnickel(II) Derivative of the Pentamethyl Ester by 2H-NMR Spectroscopy (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1725-1738 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A methylnickel(II) derivative of coenzyme F430 (1) was proposed as an intermediate in the enzymic process catalyzed by methyl-CoM reductasc. Indirect evidence points to formation of CH3-F430MII in the reaction of F30M1 (obtained from F430MII (2)) with eleclrophilic methyl donors. The results presented here show, that such a compound does exist. A paramagnetic CD3-NiII derivative 5b of the pentamethyl ester 2 (F430M) of coenzyme F430 was prepared by in situ methylation with (CD3)2Mg and characterized by its isotropically shifted 2H-NMR spectrum. At -40°, the very broad D-signal of the axially coordinated CD3 group is found at -490 ppm. Comparison with the 2H- and 1H-NMR spectra of mcthyl(tetramethylcyclam)nickel(II) derivatives 4 ([NiII(CH3))(tmc)]CF3SO3 (4a) is the only isolated CH3-Ni derivative of a N4macrocyclic NiII complex' shows that the large isotropic shift to high field is characteristic for a Me group axially bound to the Ni center. The temperature dependence of the isotropic shift of the CD3-Ni group in both 4b and 5b follows Curie's law and yields 2H hyperfine coupling constants of -0.65 (4b) and -0.85 MHz (5b), respectively. The 1H-NMR spectrum indicates that, in contrast to the five-coordinate monochloro complex [NiIICl(tmc)]+, intermolecular exchange of the axial ligand in [NiII(CH3)(tmc)]+ 4a is either slow at the NMR time scale or does not occur at all.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19910740814
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  • 6
    Digitale Medien
    Digitale Medien
    A proposal for the representation of the stereochemistry of quadrivalent centers (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 4 (1992), S. 274-278 
    Details
    ISSN: 0899-0042
    Schlagwort(e): one-wedge diagram ; structure representation ; stereochemistry ; absolute configuration ; chiral center ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The broken wedge, broken line, solid bar, and broken bar are either not reasonable or can be replaced by only one type of solid wedge in the stereochemical formulation. A convention based on a one-wedge symbolization is proposed, where a or b is used instead of c, d, e, f, g, or h. © 1992 Wiley-Liss, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/chir.530040503
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