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  • 1980-1984  (10)
  • 1970-1974  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    Methoden und Anwendungen der kernmagnetischen Doppelresonanz (1971)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 83 (1971), S. 470-489 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In Doppelresonanzspektren werden Übergänge zwischen Energieniveaus eines Kernspinsystems in Gegenwart zweier (oder auch mehrerer) oszillierender Magnetfelder gemessen. Auf solchen Experimenten beruht eine der heute wichtigsten Meßtechniken der NMR-Spektroskopie. Je nach der gewählten Methode lassen sie sich zur Entwirrung komplexer Spektren, zur Bestimmung verdeckter oder intensitätsschwacher Resonanzen, zur Ermittlung der relativen Vorzeichen von Kopplungskonstanten, bei stereochemischen oder kinetischen Untersuchungen einsetzen. Dieser breite, sich ständig erweiternde Anwendungsbereich der Doppelresonanz wird anhand spezifischer Beispiele erläutert.
    Additional Material: 29 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19710831303
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  • 2
    Electronic Resource
    Electronic Resource
    Conformational Dependence of One-Bond Cα,H Spin Coupling in Cyclic Peptides13C-NMR, Spectroscopy, Part XXIX; part XXVIII see [1].Dedicated to Prof. Conrad Hans Eugster on the occasion of his 60th birthday (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 976-988 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational effects on the one-bond Cα, H coupling constant have been studied in cyclic oligopeptides containing glycine, alanine, sarcosine and proline. The conformational contribution to 1J (Cα, H) can be described as being composed of a positive hyperconjugative term from the neighbouring N-pz orbital and a negative one from the carbonyl π-system. For glycyl units, a quantitative relation between 1J (Cα,H) and the vicinal interorbital angles Φ′ and Ψ′ is derived with maximum values ΔJ (Ψ′) = + 14.0 Hz and ΔJ (Ψ′) = -4.9 Hz. Applications to conformational analysis of cyclo (L-Pro-Gly)3, cyclo (D-Ala-D-Ala-L-Ala-D-Ala-L-Ala-L-Ala) and cyclo (Sar)8 are presented.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640404
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  • 3
    Electronic Resource
    Electronic Resource
    Direct Observation of 103Rh-Chemical Shifts in Mono- and Dinuclear Olefin ComplexesTransition Metal NMR. Spectroscopy, Part III; Part II see [1]. (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 26-45 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 103Rh-resonance has been investigated at 2.8 MHz in mono- and dinuclear olefin complexes by steady-state NMR.-pulse techniques. For dirhodium complexes with scalar Rh, Rh-coupling, a selective rf-irradiation was applied to improve sensitivity. Within the same measuring time the signal/noise ratio is improved by the factor (T2/T2*)1/2 by this steady-state method in comparison with the usual free-induction technique. (T1/T2)-ratios, as obtained from the dependence of signal in tensity on the pulse-flip angle are discussed in terms of relaxation mechanisms and chemical exchange phenomena. From (T1/T2)- and (T1 + T2)-experiments, individual T1 and T2 values have been determined for C5H5RhC8H12 and Rh(acac)3.The 103Rh-chemical shifts of 39 olefin complexes are reported. Shielding depends upon the (formal) oxidation state of Rh whereby resonances of pure olefin complexes appear at the low-frequency end of the δ-scale, which extends over 10000 ppm. For cyclic 1,3-diene ligands Rh-shielding increases with decreasing ring size and decreases with further conjugation of the diene systems.In the dirhodium complexes, Rh, Rh spin-coupling constants are 〈 10 Hz. Rh, C-coupling constants in (diene)RhCp-complexes increase, for the terminal diene C-at om, with increasing ring size of the 1,3-diene, 1J(Rh, C) = 11.7 to 17.4 Hz.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650105
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  • 4
    Electronic Resource
    Electronic Resource
    15N-NMR Spectra of Azoles with Two Heteroatoms15N-NMR Spectroscopy, Part X. For Part IX see [1]. (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 1537-1555 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 15N-NMR spectra of azoles, with natural isotope abundance, have been measured under different experimental conditions, and chemical shifts are reported for imidazoles, pyrazoles, oxazoles, isoxazoles, thiazoles, and isothiazoles. General trends of substituent effects in this heterocyclic series are discussed based on the data of 67 substituted azoles, dihydro- and tetrahydroazoles. 15N, 1H spin-coupling constants have been determined from spectra obtained by [1H] → 15N polarizationtransfer experiments, i.e. an application of INEPT and DEPT pulse sequences. Two-bond and three-bond coupling constants are fully assigned and are discussed in terms of the specific pathways in azoles. The potential of structural applications of the new data is illustrated for isomeric nitro-imidazoles and highly-substituted pyrazoles, and in the case of ring-chain tautomerism of 2-substituted tetrahydrooxazoles.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660522
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  • 5
    Electronic Resource
    Electronic Resource
    15N-NMR study of activated enamines15N-NMR Spectroscopy, Part XI; Part X: [1].. Structural dependence of δ (15N) and nJ(N,H) in primary, secondary and tertiary enamino-ketones, esters and amides (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 2113-2128 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pulse sequence INEPT was used to obtain proton-coupled 15N-NMR spectra in natural isotope abundance for enamines substituted in 2-position with electron-with-drawing groups.The chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as multiple N-alkyl substitution, double-bond configuration, H-bonding, N-lone-pair delocalization within the conjugated system, and steric effects.It is concluded that 15N chemical shifts are a sensitive probe for local structural modifications at the N-atom and conformational changes in a remote part of a conjugated molecule, while one-bond N,H-coupling essentially reflects N-hybridization and subtle local geometric distortions. Stereospecific three-bond N,H spin coupling to olefinic protons (4.0 ± 0.2 Hz) has been found a characteristic feature of (Z)-isomers in all investigated compounds, whereas two-bond coupling to olefinic protons (2J(N,H) = 0.5 to 5 Hz) is observed in (E)-isomers. The sensitivity to solvents and steric properties of remote substituents renders geminal coupling a useful probe for studying electronic effects in the C—N bond.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660722
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  • 6
    Electronic Resource
    Electronic Resource
    Studies on the Stereochemistry of 2-(Nitromethylidene)-HeterocyclesContribution No. 57 from the Research Centre.Nitroenamines, Part X. For Part IX see [1]. (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1669-1680 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H-NMR spectra of 2-(nitromethylidene)pyrrolidine (7), 1-methyl-2-(nitromethylidene)imidazolidind (10) and 3-(nitromethylidene)tetrahydrothiazine (11) in CDCl3 and (CD3)2SO indicate that these compounds have the intramolecularly H-bonded structures (Z)-7, (E)-10 and (Z)-11 while the N-methyl derivative 8 of 7 is (E)-configurated in both solvents. 1-Benzylamino-1-(methyltio)-2-nitroehtylene (13), an acylic model, has the H-bonded configuration (E)-13 in CDCl3 and in (CD3)2SO. 2-(Nitromethylidene)thiazolidine (3) has the (E)-configuration in CDCl3 but exists in (CD3)2SO as a mixture of (Z)- and (E)-isomers with the former predominating. Both species are detected to varying proportions in a mixture of the two solvents. 15N-NMR spectroscopy of 3 ruled out unambiguously the nitronic acid structure 6 and the nitromethyleimine structure 5. The N-methyl derivative 4 of 3 is (Z)-configurated in (CD3)2SO. Comparison of the olefinic proton shifts of (Z)-3 and (Z)-4 with those of analogues and also of 1,1-bis(methylti)-2-nitroethylene (12) shows decreased conjugation of the lone pair of electrons of the ring N-atom in (Z)-3 and (Z)-4. This is also supported by 13C-NMR studies. Plausible explanations for the phenomenon are offered by postulating that the ring N-atoms are pyramidal in (Z)-3 and (Z)-4 and planar in other cases or, alternatively, that the conjugated nitroenamine system gets twisted due to steric interaction between the NO2-group and the ring S-atom. Single-crystal X-ray studies of 3 and 8 show that the former exists in the (Z)-configuration and the latter in (E)-configuration; the ring N-atom in the former has slightly more pyramidal character than in the latter.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670702
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  • 7
    Electronic Resource
    Electronic Resource
    One-Bond 13C, 13C-Spin Coupling in η4-, η3- and η2-Olefin Transition Metal Complexes13C-NMR. Spectroscopy, Part XXXI; Part XXX: [1]. (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 2378-2382 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: One-bond 13C, 13C-spin-coupling constants have been measured, with natural isotope abundance, in η4-diene, η3-allyl and η2-ene transition-metal carbonyl complexes. Typical values of 1J(C,C) are given for Fe-, Ru- and Os-complexes with the three types of olefinic ligands. The effects of substituents and the structural significance of the C,C-coupling constants are discussed.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640744
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  • 8
    Electronic Resource
    Electronic Resource
    Dimetallic Complexes with Bridging Seven-membered Cycloolefins. Synthesis, Multinuclear NMR.-Spectroscopic Properties and StructureReactivity of Complexed Carbocycles, Part XIV; Part XIII see [1]; Transition Metal NMR. Spectroscopy Part IV; Part III see [2]. (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 1145-1157 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of dimetallic olefin complexes of the type L1M1C7H7M2L2 (M1 = Fe, Co, Rh; M2 = Rh, Ir, Pd; L1 = CO, C5H5; L2 = diene, allyl, P(OR)3) is described. The fluxional structures were investigated by 13C-, 57Fe- and 103Rh-NMR.-spectroscopy, and a cisoid dimetallic coordination, including a (metal, metal)-bond, can be deduced for the C7H7-ring. 57Fe- and 103Rh-chemical shifts give indications for the charge distribution in the 34e-complexes. The homodimetallic complex (Cp)Rh(tropone)Rh(Cp) (13, Cp = cyclopentadienyl) and the corresponding 2-methoxytropone complex 14 were synthesized in addition to the above mentioned complexes. A fluxional bis(1-3-η-allyl)-coordination of the two Rh-atoms was derived from the temperature-dependent 13C-NMR.-spectra. A spin simulation of the (Cp)-multiplets of 12 and 13 yields information about (Rh, Rh)-spin-coupling which amounts to ≈5 Hz at 30°.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650404
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  • 9
    Electronic Resource
    Electronic Resource
    Solvent-Induced Deuterium Isotope Effects in 13C- and 15N-NMR. Spectra of Enaminones15N-NMR. Spectorscopy, Part IX; Part VIII: [1]. (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 2077-2087 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of deuterium on the 13C and 15N chemical shifts of enaminones has been investigated. D/H isotope shifts are reported for neutral and protonated species, i.e., when the isotope is exchanged on the C(2)-, N-, or O-atoms. In cases of slow exchange the isotope shifts were obtained from solutions containing both isotopomers, whereas for fast exchange (acidic solutions) either separate NMR. sample tubes (15N-NMR.) or coaxial tubes (13C-NMR.) were used.In neutral molecules the isotope effects δC(D, H) are intrinsic in nature. In acidic solutions, the enaminocarbonyl cations formed exhibit δC(D, H)- and δN(D, H)-values which are discussed in terms of the proton transfer. The mesomeric character of the cations is reflected by characteristic features in the δC(D, H)- and δN(D, H)-values, which can be ascribed to isotopic perturbation of resonance.O-Protonation shifts in the 15N-resonance, observed for the first time, are large and positive (+60 to +76 ppm), in contrast to amides, where the effects are of the same sign but an order of magnitude smaller. Both protonation shifts and solvent-induced isotope effects are discussed in connection with the nucleophilic character of the reactive centers in the enaminone synthon.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650715
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  • 10
    Electronic Resource
    Electronic Resource
    (Butadiene)tricarbonylosmium13C-NMR. Spectroscopy, Part XXVI, Part XXV [1]. synthesis and structural comparison with the Fe- and Ru-complexes based on 1H- and 13C-NMR. Spectroscopy (1980)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 63 (1980), S. 773-779 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photochemical synthesis of the title complex from 1,3-butadiene and dodecacarbonyltriosmium is described. The 1H-NMR. and H-coupled 13C-NMR. spectra are analyzed completely and the H, H- and C,H-coupling constants compared with the data of the corresponding Fe- and Ru-complexes. One-bond 13C, 13C-coupling constants are reported for a series of complexed 1,3-dienes. All data are consistent with an increasing distortion from planarity of the C,H-skeleton at the terminal diene C-atoms in the sequence Fe → Ru → Os.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19800630404
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