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  • Analytical Chemistry and Spectroscopy  (98)
  • 1980-1984  (98)
  • 1981  (98)
  • 11
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 268-272 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An equation has been developed which relates ortho or C-β 13C substituent chemical shifts (SCS) to the ortho proton-proton coupling constant in the unsubstituted member of a conjugated series. This method is an extension of previous equations which have been used to predict ortho 1H SCS values, and has its origin in a relationship between bond order and SCS values. The equation was derived from ortho 13C data in 2-naphthalenes and monosubstituted benzenes and its application to other unsaturated series is discussed.
    Additional Material: 3 Tab.
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  • 12
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 273-274 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational equilibrium constants for a series of 1-alkyl substituted cyclohexanols have been determined using a lanthanide shift reagent, and the results compared with other methods. In comparison to other technique greater preference is shown by the hydroxyl group for the equatorial position. This is rationalized by the effect on the equilibrium of the bulky shift reagent.
    Additional Material: 4 Tab.
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  • 13
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 344-346 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An indirect method is employed for determining the 15N parameters at the natural abundance level in a series of simple acyclic and cyclic amides. The one bond coupling constant, 1J(15N1H), and the 15N chemical shift are measured as a function of the carbonyl substituent group or the ring size and the nature of the solvent (CCl4 or H2O). These 15N parameters are related to the amide bond structure, the nitrogen configuration and possible intermolecular hydrogen bonding (amide-amide or amide-water).
    Additional Material: 2 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 131-133 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR spectra of four thiocarbamates and their corresponding S-oxides and S, S-dioxides are reported. Both βSO and βSO2 effects are deshielding and range from 20.44 to 21.68 ppm. The βSO′ effects are slightly deshielding (0.20 ∼ 0.0.77 ppm). The β′SO2 effects, on the contrary, are shielding and range from -6.54 to -6.98 ppm. The γ′, δ′, ξ′, and ζ′ effects are also discussed.
    Additional Material: 3 Tab.
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  • 15
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 16 (1981), S. 60-62 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spin-lattice relaxation rates of the 13C responses of pyridine were measured in the presence of aqueous sucrose and sodium alginate solutions and calcium alginate gels. In each case the results indicated a reduction in the overall tumbling rate of pyridine compared with that in aqueous media due to molecular association with the carbohydrate. Although anisotropic motion about the C-4:N axis of pyridine was apparent in the sucrose solutions no consistent trends were observed for the alginate samples.
    Additional Material: 3 Tab.
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  • 16
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 180-181 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nitrogen-15 NMR spectra of 11 ketenimines have been taken both at the natural-abundance level of 15N and with the aid of 15N-labeling. The nitrogen chemical shifts are substantially different from those of neutral imines and are upfield, more like those of protonated imines. The results are in accord with significant delocalization of the nitrogen lone-pair. Furthermore, there is a rough parallelism between the 13C shifts of the terminal carbons and the 15N shifts.
    Additional Material: 1 Tab.
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  • 17
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 214-216 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 270 MHz1H and 22.6 MHz13C NMR spectra of the tripeptide (L-Ser)3 dissolved in D2O have been measured and completely analysed as a function of pD in the region from 1.1 to 10. The pK(NH2)=7.0 is distinctly lower than common values for N-terminal residues. The chemical shifts for the peptide seryl residue change little with pD, with the H-β1 and H-β2 resonances being differently affected by the ionization of the COOH and NH2 groups. The 13C-α chemical shift in the peptide seryl residue exhibits a sequence effect which is considerably larger than expected on the basis of recently reported mean shifts. Rotational isomerism about the C-α—C-β bond is studied for the three different Ser residues on the basis of vicinal coupling constants 3J(H-α, H-β), and it is found that the population pb (-OH gauche to -CO-, and trans to -NH-) in the N- and p-Ser residues is notably larger than pb in Ser and Acetyl-Ser. In. C-Ser, In. C-Ser, pb is comparable to pb in Ser, but is twice as large as pb in AcSer.
    Additional Material: 4 Tab.
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  • 18
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 285-289 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C NMR spin-lattice relaxation times (T1) and nuclear Overhauser enhancements (η) were measured for dithiarsolanes. The contributions of dipolar (T1DD) and spin-rotation (T1SR) mechanisms were determined. The T1 data were analysed to obtain information on the relative order of magnitude of the internal motion rates. The calculations were based on the isotropic, with internal rotation about the As—Ph bond, model of reorientation. In cis, trans-2-phenyl-4-methyl-1,3,2-dithiarsolane, the internal rotation of the phenyl ring is c. three times faster than overall molecular reorientation. The internal motion of the arsolane ring is slightly slower than the phenyl ring rotation. The rotation of the methyl groups in the compounds appears to be considerably hindered, with rotation energy barriers of c. 10 kJ mol-1. In contrast to the situation in the 4-methyldithiarsolane, the internal motion of the arsolane ring is twice as fast as the internal rotation of the phenyl ring for the methyl-unsubstituted analogue, 2-phenyl-1,3,2-dithiarsolane.
    Additional Material: 4 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 123-124 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mass spectra of four tetrabenzo[b, d, h, j][1, 6]diazacyclododecines are reported. The common pattern of fragmentation is altered by the presence of ortho methoxycarbonyl groups.
    Additional Material: 4 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 176-179 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical ionization mass spectrometry and mass analyzed ion kinetic energy spectrometry in conjunction with collision induced dissociation are used to study the fragmentation behavior of a series of α,ω-hydroxyalkylamines. The difference between the ionic population present at equilibrium in the source, and that which is sampled under nonequilibrium conditions, is revealed in the striking differences observed in product distributions in the chemical ionization mass spectra and the mass analyzed ion kinetic energy spectra. The major fragmentations in the mass analyzed ion kinetic energy spectra, loss of NH3 and H2O, show large variations in intensity as a function of the chain length between the hydroxy and amino functionalities. These results are rationalized through analysis of the relevant thermochemical data.
    Additional Material: 3 Ill.
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