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  • 1
    Digitale Medien
    Digitale Medien
    Electron spin resonance spectroscopy of free radicals (1993)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 31 (1993), S. 1027-1030 
    Details
    ISSN: 0749-1581
    Schlagwort(e): ESR ; Isotropic spectra ; Powder spectra ; Dithiadiazolyl radicals ; Dimerization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Solution and powder ESR spectra of the 4-trifluoromethyl-1,2,3,5-dithiadiazolyl and 4-pentafluorophenyl-1,2,3,5-dithiadiazolyl free radicals were analysed. Comparison of the ESR parameters with those obtained for the protonated equivalents shows that fluorination produces a drift of unpaired electron spin density away from the nitrogen 2px orbitals towards sulphur 3px orbitals (x is the direction perpendicular to the heterocyclic ring), consistent with an increase in electronegativity of the substituent. The fluorinated radicals dimerize more readily than their protonated counterparts.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260311114
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  • 2
    Digitale Medien
    Digitale Medien
    ESR spectroscopy of some dicyano-, pyrazino- and quinoxalino-1,3,2-dithiazolyl radicals (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 774-778 
    Details
    ISSN: 0749-1581
    Schlagwort(e): ESR ; 1,3,2-Dithiazol-2-yl radicals ; Pyrazine ; Quinoxaline ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Several symmetrical 1,3,2-dithiazol-2-yl radicals have been examined that have in common nitrogen-containing substituents at the 4- and 5-positions, namely 4,5-dicyano-1,3,2-dithiazol-2-yl, [15N2]-1,3,2-dithiazolo [4,5-b] pyrazin-2-yl and 1,3,2-dithiazoleo [4,5-b] quinoxalin-2-yl. The ESR spectrum of the 4,5-dicyano radical does not reveal any 14N splittings from the cyanide groups; however, the pyrazine and the quinoxaline derivatives do have multi-lined well resolved spectra arising from substantial hyperfine interactions with these nuclei. The interactions are sufficiently large to be observed in the powder spectra of the latter. The presence of proton hyperfine interactions shows that unpaired-electron spin density is delocalized over all the rings. It has been found that the radicals attached to pyrazine and quinoxaline can be incorporated into single crystals of naphthalene and phenazine, respectively.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260300814
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  • 3
    Digitale Medien
    Digitale Medien
    EPR study of iron - nitrosyl clusters in the oxidation of Fe(NO)2(CO)2Presented at the ‘L. H. Sutcliffe’ Symposium on Magnetic Resonance, University of Surrey, 24 March 1995.NRCC No. 37313. (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. S14 
    Details
    ISSN: 0749-1581
    Schlagwort(e): EPR ; ESR ; iron-nitrosyl radicals ; cluster nitrosyls ; Fe(NO)2+ ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The oxidation of Fe(NO)2(CO)2 by tetracyanoethylene (TCNE), by the nitrosonium ion (NO+), or by electrolysis in polar solvents was studied by EPR spectroscopy. A number of long-lived (τ1/2 of the order of hours) free radicals were detected in the early stages of reaction, all having similar isotropic g-factors and 14,15N hyperfine interactions. These have been identified as the mononuclear cations, Fe(NO)2(CO)2-nStn+ (St = solvent molecule). They slowly disappear and are replaced by persistent radicals (τ1/2 of the order of days) that show equal isotropic hyperfine interactions with four-, six- or eight-nitrogen nuclei. Infrared and EPR spectroscopic data suggest that two of these species are trinuclear nitrosyl clusters, Fe3(NO)2n(CO)(12-3n)+ (n = 3, 4), in which the unpaired spin is localized on one iron nucleus, but which are fluxional on the EPR time-scale. The third nitrosyl radical with four equivalent NO ligands is tentatively identified as a binuclear intermediate that may be a precursor of the trinuclear clusters.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260331305
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  • 4
    Digitale Medien
    Digitale Medien
    ESR spectroscopy of the 4,5-bis(methoxycarbonyl)-1,3,2-dithiazol-2-yl radical labelled with sulphur-33 and nitrogen-15 (1988)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 26 (1988), S. 755-759 
    Details
    ISSN: 0749-1581
    Schlagwort(e): ESR ; 1,3,2-Dithiazol-2-yl radicals ; 33S-labelled free radicals ; Energy calculations of conformers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A derivative of the 1,3,2-dithiazol-2-yl radical was labelled with 33S in order to evaluate the p spin densities on the sulphur atoms. This information is required to provide a full description of the SOMO which, in turn, aids the understanding of the structure of the radical dimers. An unexpected result is that the two sulphur atoms are non-equivalent in the solid state. Calculations suggest that this is due to out-of-plane twisting of the substituent groups. Comparison of the ESR parameters of the bis(methoxycarbonyl) derivative with other members of the 1,3,2-dithiazol-2-yl group of radicals (including the parent radical) shows that it is a good model for the whole group.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/mrc.1260260906
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