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  • Analytical Chemistry and Spectroscopy  (963)
  • 1980-1984  (963)
  • 1981  (963)
  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 1-6 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Detailed 1H NMR studies of ms tetraphenylchlorins (H2TPC), new amino- and hydroxypyrroline substituted ms tetraphenylchlorins and ms tetraphenylisobacteriochlorins (H2TPisoB) are presented and discussed. The results obtained are consistent with the general aspects of the ring current models as applied to the parent porphyrins. According to proton chemical shifts a gradual reduction in the magnitude of the ring current is observed in the order ms tetraphenylporphyrin (H2TPP) 〉 H2TPC〉 ms tetraphenylbacteriochlorin (H2TPB) 〉 H2TPisoB. The 1H NMR spectra show chemical non-equivalence of the pyrroline ring protons due to adjacent substituents, and effects of steric constraints on the aminoalkyl substituents due to the close vicinity to the meso phenyl rings. The non-equivalence of the methylene protons of the pyrroline ring produces geminal coupling between the two methylene protons and vicinal coupling with the adjacent pyrroline proton, more pronounced in H2TPC—OH and in . Restricted configuration of the methylene groups in the ethyl groups of H2TPC—C(H)(CH3)N(CH2CH3)2 produces observable geminal coupling between the methylene protons. 1H NMR reveals the difference between two types of meso phenyls in the chlorins, and three types of meso phenyls in isobacteriochlorins, as reflected in the chemical shifts of the o-phenyl protons.
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  • 2
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 22-24 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C chemical shifts obtained under uniform conditions for selected compounds containing secondary aliphatic fragments were employed in a linear regression analysis. Two-parameter relationships describing the substituent effects in the saturated framework were calculated, and the usefulness of such calculations is discussed. Finally, coefficients for linear relationships in primary and secondary alkyl derivatives are compared.
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  • 3
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: J(13C1H) coupling constants for some methyl- and aminopyrimidines have been determined by 13C NMR. Both the one-bond and long-bond and long-range coupling constants follow general trends which can be summarized in a few simple rules. In particular, the 3J(C-i,H) coupling constants between a ring carbon C-i and the ring protons are larger than the 2J(C-i,H) coupling constants. The opposite is observed for the couplings between the ring carbons and the methyl protons: 3J(C,Me). These general rules are very useful for the assignment of resonances in complex 13C spectra of pyrimidines and seem to be valid for other 6-membered aromatic nitrogen heterocycles. Furthermore, the additivity of substituent effects on 1J (CH) for monosubstituted pyrimidines allows the estimation of 1J (CH) for polysubstituted pyrimidines with a very good accuracy.
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  • 4
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 15NMR chemical shifts were measured of a number of N-substituted formamides and acetamides at the natural abundance level. The ratios of the cis and trans isomers for several N-alkylformamides were also determined. Substituent effects on the 15N chemical shifts of formamides are compared with those of some other nitrogen-containing compounds. There is a consistent pattern of behavior of the one bond spin-spin coupling constants [1J(15NH)] wherein the trans isomers of N-alkylformamides are larger than those of the cis isomers.
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  • 5
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    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 13-17 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H spectrum of (15N)acetamide has been measured in dimethyl sulphoxide (DMSO), methyl propyl ketone (MPK), 1,3-dioxane, 1,4-dioxane, D2O, acetonitrile and pyridine-d5 at various temperature intervals within the range of 278-343 K. From the temperature dependence of the NMR spectra of the amide protons, the free energy of activation, ΔG≠, for hindered rotation about the central C—N bond was determined by means of total line shape analysis in the four solvents DMSO, MPK and the two dioxanes. Observed values of ΔG≠ (298 K) (72.7 in DMSO, 70.1 in MPK, 70.0 in 1,3-dioxane and 70.1 kJ mol1 in 1,4-dioxane) were not very sensitive to the choice of solvent or concentration. The concentration dependence of the internal chemical shift between the amide protons was studied in MPK, D2O, acetonitrile and pyridine-d5. The free energy of activation and the internal chemical shift are discussed on the basis of solvent-amide and amide-amide specific hydrogen bonding interactions, and in comparison to the results of molecular orbital calculations.
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  • 6
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    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 29-32 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H and 31P NMR spectra of the phenyl ester of dichlorophosphoric acid dissolved in Merck nematic phase IV have been recorded and analysed. The values of the dipole dipole couplings have been discussed in terms of several different geometric models. Non-planarity of C-1, O, P and the phenyl ring must be assumed in order to account for the results; a twist angle of 49° was found.
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  • 7
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The NMR variable temperature behaviour of N-aroyl- and N-thioaroyl-N′-piperonylpiperazines was investigated. The largest chemical shift separation between the exchanging methylene groups, and the highest energy barrier, is found for the thioamide compounds. Results from semi-empirical calculations are qualitatively in line with the experimental findings, revealing that the higher barrier in the thiocarbonyl compounds compared with the carbonyl compounds is mainly connected with differences in the energies of ground states, rather than in those of transition states, of these molecules. The effect of the nature of the heterocyclic ring containing the amidic nitrogen atom on the barrier height is also discussed.
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  • 8
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    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 37-42 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The olefins Ph2P(X)CH=CHR [X=lone pair, O, S, Ch3I; R=Ch3, ph, P(X)ph2] have been prepared and their 1H, 13C and 31P NMR spectra measured. trans 3J[P(IV)C] (range 18.3-25.7 Hz) is greater than cis 3J[P(IV)C] (range 6.9-11 Hz) but this relationship does not hold for P(III) compounds. In the 31P spectra the E isomer absorbs to higher field than the Z isomer for P(III) and P(IV) compounds. The 1H data are in accord with previous results; average substituent shielding coefficients for ph2P(X) substituted alkenes are reported.
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  • 9
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The lanthanide shift reagent (LSR)/1H NMR study of some 7-chloro-5-phenyl-2,3-dihydro-1 H-1, 4-benzodiazepines shows that these compounds exist in CDCI3 solution as two pseudo-boat conformers, rapidly interconverting at room temperature. Computer simulated lanthanide induced shifts (LIS) are consistent with LSR complexation by the imine nitrogen atom. The lanthanide shifts the conformational equilibrium towards conformer (a), with a pseudoequatorial 1-substituent: this effect may be the result of the greater basicity of 4-N when the 1-N lone pair is pseudoaxially directed, thus permitting an extended electron delocalization from 1- to 4-N through the fused benzene ring. The detection of H-9/1-Me through space spin-spin coupling in medazepam (7-chloro-1-methyl-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepine) supports the observed higher availability of conformer (a) to LSR. A LIS computer calculation to predict the population ratio results in reasonable agreement with the conformational changes based on the response of 3J(HH) to lanthanide addition. The electronic and steric effects which determine the greater stability of conformer (a) may be effective in the drug-receptor interaction.
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  • 10
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    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 53-56 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sodium borohydride reduction of methylphenobarbital leads to the formation of two different dihydroderivatives, reduced either in position 4 or position 6. The structures of the derivatives have been determined through analysis of the 1H and 13C NMR spectra of phenobarbital, methylphenobarbital and their derivatives. Detailed interpretation of the spectra and the resulting spectral parameters indicate conformations where the hydroxyl groups are axial and trans to the ethyl group. In these configurations the phenyl ring becomes equatorial. The results also allow an unambiguous assignment of the resonances of the phenyl carbons 2′(6′) and 3′(5′) of phenobarbital and the carbonyl carbons 4 and 6 of methylphenobarbital, differing interpretations having been previously advanced in the literature.
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  • 11
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relationship between vicinal NMR proton-proton coupling constants and the pseudorotational properties of the sugar ring in nucleosides and nucleotides is reinvestigated. Compared with our earlier study several important improvements are introduced: first, a new empirical generalization of the classical Karplus equation is utilized, which allows an accurate correction for the effects of electronegativity and orientation of substituents on 3J(HH); second, empirical correlations between the parameters governing the conformation of β-D-furanosides (taken from an analysis of 178 crystal structures) were used to define proton-proton torsion angles as a function of the pseudorotation parameters P and Φm; and, third an iterative least-squares computer program was devised to obtain the best fit of the conformational parameters to the experimental coupling constants. NMR data for the sugar ring in the following compounds were taken from the literature and analysed: 3′,5′-cyclic nucleotides, a base-stacked ribonucleotide, 2′-anhydroarabinonucleosides, α-D-2′,2-O-cyclouridine, 2′- and 3′-aminosubstituted ribonucleosides, 2′- and 3′-deoxyribonucleosides. The present results confirm that the conformational properties found in the solid state are, on the whole, preserved in solution.
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  • 12
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    Organic Magnetic Resonance 15 (1981), S. 68-71 
    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 20 aminocycloalkanecarbonitriles were determined in CDCl3. The signals were assigned by a self-consistent analysis of chemical shift data and comparison with results from phencyclidine analogues. The results were interpreted in terms of changes in the amine (primary, secondary, tertiary) and the cycloakane (cyclohexane vs cyclopentane) moieties and their bulk. Changes in the conformational equilibria of the cyclohexane series are suggested by comparisons between data from the carbonitrile and phencyclidine series. The spectra are suitable for corroborative authentication of reference materials and the identification of unknowns.
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  • 13
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A useful and reliable procedure has been developed for the evaluation of the structures of organic nitriles using lanthanide shift reagents. The procedure is based on a statistical comparison of the experimental lanthanide induced shifts (LIS) with values which are predicted with the pseudocontact equation for a proposed structure. The experimental LIS are obtained by nonlinear regression analysis of the chemical shifts observed in the presence of varying amounts of the shift reagent, Eu(fod)3. The precise geometry for a proposed structure is obtained from molecular mechanics calculations. The LIS are then predicted with the pseudocontact equation using k=976.6 and a europium-nitrogen bond length of 2.50 Å. (Detailed arguments are presented in support of these values.) The carbon-nitrogen-europium array is approximately linear, although small distortions from linearity are both expected and observed.
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  • 14
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    Organic Magnetic Resonance 15 (1981), S. 72-77 
    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 all cations obtained by methylation at sulphur of the mono-and dimethylthiolanes are reported. The methyl substituent on sulphur affects the shieldings of the adjacent carbons in a manner which allows easy identification of the cis and trans isomers. For most compounds the 13C pattern is consistent with a half-chair ring conformation with maximum staggering at C-3, C-4. Only with methyl groups at the 1,2-or 1,2,3-positions is the half-chair appreciably deformed. It is suggested that in these cases the preferred conformation is a quasi-envelope with C-3 at the top.
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  • 15
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    Organic Magnetic Resonance 15 (1981), S. 87-93 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H NMR spectral analysis of four 8-membered rings, 2-thioxo- (or 2-oxo-) 2-R-1,3,6,2- trithiaphocane, is reported. The stereochemistry of the 8-membered ring is discussed. The 31P NMR spectral parameters [δ31P, 1J(PC)] obtained on several cyclic 1,3,2-dithiaphospha compounds of variable size (5, 6, 8, 12 and 16-membered rings) are discussed as a function of the ring size and of the geometry of the molecule.
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  • 16
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    Organic Magnetic Resonance 15 (1981), S. 78-82 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical shifts of H-bonded protons in tetrabutylammonium hydrogen maleate and 14-substituted picolinic acid N-oxides have been measured in a number of dry solvents, of different activity, in order to distinguish between symmetrical single minimum and asymmetrical hydrogen bonds. In tetrabutylammonium hydrogen maleate the resonance was observed at 20.70 ppm and its was independent of the nature of the solvent used. The chemical shift value of picolinic acid N-oxide varies with the solvent. These observations suggest that the hydrogen bond is symmetrical in tetrabutylammonium hydrogen maleate but that it is asymmetrical in picolinic acid N-oxide. The chemical shifts of substituted picolinic acid N-oxides were correlated with σp, σm and ΔpKa. The substituent and solvent effects are compared and the position of the intramolecular H-bonded protons in picolinic acid N-oxides are estimated and discussed.
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  • 17
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the reactions of alkyl-substituted-benzenecarboxylic and -2-hydroxybenzenecarboxylic acids (ArCOOH) with alkyl-substituted phenyl Grignard reagents (RMgX) in the presence of nickel, ketyl radicals Ar—CO-—R are formed. The para substituents (H, Me, Et, Isopr and t-Bu) of R increase the non-equivalence of its ortho protons (a change of a2H = 0.43 mT, a6H = 0.422 mT to 0.435 mT, 0.395mT respectively, on substituting t-butyl for H at position 4). The oxido anion group originating from 2-hydroxybenzenecarboxylic acid has a strong push effect and nearly doubles the unpaired spin density on the phenyl ring R.
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  • 18
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    Organic Magnetic Resonance 15 (1981), S. 94-95 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a 15N enriched macrocycle containing the ferrocene unit is descibed, and the 15N NMR spectra of the macrocycle and those of its complexes with some metallic cations are reported.
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  • 19
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    Organic Magnetic Resonance 15 (1981), S. 96-98 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vicinal and geminal 13CO2H—1H coupling constants are reported for malic and thiomalic acids at various pH values and related, in a comparative manner, to the known conformational information obtained by 1H NMR.
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  • 20
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    Organic Magnetic Resonance 15 (1981), S. 102-103 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A summary of all the one-bond carbon-carbon spin-spin coupling constants, Known up to the beginning of 1980, is given in diagrammatic form.
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  • 21
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    Organic Magnetic Resonance 15 (1981), S. 99-101 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some carbon-13 NMR signal assignments of diazepam, flurazepam, clonazepam and chlordiazepoxide have been revised and the assignments of nitrazepam are reported. The assignments of the various resonances were made by considering the changes in chemical shifts produced by the change of substituents and also by comparison with the chemical shifts of model compounds.
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  • 22
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    Organic Magnetic Resonance 15 (1981), S. 104-105 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 15N and 13C satellites in the Proton spectrum of nitromethane oriented in a lyotropic solvent have been observed. Indirect as well as direct (13CH) and (15NH) couplings have been measured and the molecular structure has been derived.
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  • 23
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    Organic Magnetic Resonance 15 (1981) 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 24
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    Organic Magnetic Resonance 15 (1981), S. 106-109 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 15N chemical shifts of 32 substituted pyridines and 19 substituted pyrimidines, together with additional data from the literature, are used to evalute substituent increments, Ai and Aik, in the respective series. Differential chemical shifts, Δδ(N), correlate with corresponding Δδ(C) values whereby, on the ppm scale, nitrogen shifts are approximately three times more sensitive towards substituents than carbon shifts. The 15N increments have proven additive and useful for assignment purposes.
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  • 25
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    Organic Magnetic Resonance 15 (1981), S. 111-130 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The non-bonded interactions which occur between solute and solvent molecules are discussed and the various models which describe the interactions are presented. The models are employed, within a quantum chemical framework, to estimate the extent of medium effects on chemical shifts and spin-spin couplings. Comparison between the calculated and available experimental data is provided for some first row nuclei.
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  • 26
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    Organic Magnetic Resonance 15 (1981), S. 131-132 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: While there is a useable paramagnetic relaxation reagent (PARR) for use in nonpolar or low polarity solvents, there has not been a practical PARR for use in highly polar solvents. A reagent, Gd(NO3)3-inositol, is described which appears to satisfy this need. The performance of the reagent is given in terms of its effect on the T1, NOE and line width values of N,N-dimethylformamide. In addition, the application of this reagent to adenosine is also reported.
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  • 27
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    Organic Magnetic Resonance 15 (1981), S. 139-142 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configuration and stable conformation of two dibenzylidene-L-iditol isomers formed upon benzalation of L-iditol, as well as that of a third isomer obtained by partial hydrolysis of the tribenzylidene derivative - the main product of the benzalation reaction - were determined by 1H and 13C NMR spectroscopy.
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  • 28
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Isomeric mixtures of compounds MenM(CH=CHMe)4-n (M=Si, Pb; n=0-3) have been prepared and studied, as well as pure Me3M(CMe=CH2) and mixtures containing propenyl isopropenyl residues bonded to silicon and lead. 1H, 13C, 29Si and 207Pb NMR data are presented; as previously observed for the corresponding tin compounds, the 29Si and 207Pb shifts for the Me3MC3H5 isomers can be used to calculate the shifts expected for the other isomers; while for lead the agreement is good, calculated and observed values for silicon diverge with decreasing n due, at least in part, to steric factors.
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  • 29
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    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.
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  • 30
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    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.
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  • 31
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    Organic Magnetic Resonance 15 (1981), S. 275-279 
    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 a series of methyl substituted 3-arylpiperidines and 4-aryl-4-piperidinols and related compounds are reported, and chemical shift data analysed in terms of the configuration and conformation of isomeric pairs. Special attention is given to the γ chemical shift parameter of axial methyl, and the effects of a nitrogen lone pair orbital and hydroxyl or acyloxy group on the chemical shifts of ring and methyl carbons.
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  • 32
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    Organic Magnetic Resonance 15 (1981), S. 285-287 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR spectra of 24 N-alkynyl cyclic amines were analysed. The effect of substituting the acetylenic proton by n-butyl, tert-butyl and phenyl groups was determined.
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  • 33
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    Organic Magnetic Resonance 15 (1981), S. 280-284 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H and 13C NMR spectra of 8-hydroxyquinoline (oxine) and its 5-Me, 5-F, 5-Cl, 5-Br and 5-NO2 derivatives have been studied in DMSO-d6 solution. The 1H and 13C chemical shifts and proton-proton, proton-fluorine, carbon-proton and carbon-fluorine coupling constants have been determined. The 1H and 13C chemical shifts have been correlated with the charge densities on the hydrogen and carbon atoms calculated by the CNDO/2 method. The correlation of the 1H and 13C chemical shifts with the total charge densities on the carbon atoms is approximately linear (rH2 = 0.85, rC2 = 0.84). The proton in peri position to the nitro group in 5-NO2-oxine is an exception.
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  • 34
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    Organic Magnetic Resonance 15 (1981), S. 288-293 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H, 2H and 13C NMR studies of cyclobutene and a series of isotopically enriched species have led to a determination of the 1H—1H, 13C—1H, 13C—2H and 13C—13C coupling constants in these compounds. In agreement with general observations, 1J(CH) is found to depend on the hybridization of the carbon atoms. Likewise, 2J(HH), 2J(CC), 3J(HH) and 3J(CH), but not 2J(CH), depend on the angles between the bonds connecting the coupled nuclei. When comparing cyclobutene with thiete 1,1-dioxide (thiete sulphone) an increase of almost 20 Hz is observed for 1J(C-2, H-2) in the latter compound. All but one of the observed deuterium isotope effects on chemical shifts are negative. In the case of isotope effects upon the one-bond coupling constants, the obtained values support the results of the theoretical calculations of Sergeev and Solkan.
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  • 35
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    Organic Magnetic Resonance 15 (1981), S. 294-295 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The signs of the spin-spin coupling constants between the aldehydic proton and the fluorine nuclei in pentafluorobenzaldehyde are negative over four and six formal bonds and positive over five bonds. The opposite signs had been assumed in previous studies of this molecule. The correct signs are necessary for the determination of the conformational and substituent dependence of these coupling parameters.
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  • 36
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    Organic Magnetic Resonance 15 (1981), S. 296-302 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C chemical shifts of 11 substituted triphenylamines have been determined and the assignment of these resonances made using intensities, 1H and 19F couplings and predictions from bond additivity relationships. 13C chemical shifts at carbons bearing the substituent and at carbons ortho to the substituent correlated reasonably well with the Q parameter. A multiple regression analysis of chemical shifts with the field and resonance parameters of Swain and Lupton and the Q parameter produced significantly better correlations than those obtained when Q was omitted for these positions. 13C chemical shift correlations for carbons meta and para to the substituent were not significantly better than when Q was omitted. Significant correlations were obtained between field and resonance parameters and 13C chemical shifts of C-o and C-p, and C-i, C-o, C-m and C-p of the non-substituent bearing phenyl rings in ortho- and para-substituted phenyldiphenylamines, respectively.
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  • 37
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    Topics: Chemistry and Pharmacology
    Notes: The spectra of various 1-substituted and 1,5-disubstituted anthraquinones have been studied and the chemical shifts of the different carbon nuclei determined. The chemical shifts previously reported for 1-Me-anthraquinone have been corrected and reassigned. The C-1, C-4 and C-13 shifts of 1-substituted derivatives are correlated with the chemical shifts of monosubstituted benzenes. Deviations from the regression lines can be explained by the existence of steric factors and hydrogen bonding. A three-parameter correlation with Swain and Lupton's F and R and Schaefer's Q provides relationships for the prediction of all chemical shifts of 1-substituted anthraquinones when the substituents have a cylindrical symmetry.
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  • 38
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    Organic Magnetic Resonance 15 (1981), S. 307-310 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several sulfanilamide-type compounds in their solid state have been investigated by the 14N nuclear quadrupole resonance (NQR) technique. The electron distributions at the sites of the nitrogen atoms, calculated by the Townes and Dailey theory, indicate a significant correlation between the quadrupole coupling constant for the primary amino nitrogen (N4), which is a measure of the (π-σ) electron density at N4, and the in vitro bacteriostatic activity of the sulfanilamides.
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  • 39
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    Organic Magnetic Resonance 15 (1981), S. 311-316 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The assignment of all ring carbons of p-benzoquinones derived from perezone and from thymoquinone was completed using gated decoupled spectra. The long range proton-carbon couplings are discussed in terms of the degree of substitution of the quinone ring. The tautomeric interconversion of the two energetically equivalent forms of 2,5-dihydroxy-1,4-benzoquinones has been studied in various solvents and at several temperatures.
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  • 40
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    Organic Magnetic Resonance 15 (1981), S. 317-318 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton and carbon chemical shifts for a series of tetrakis(p-substituted phenyl)ethylenes are described. Assignments followed routine substituent chemical shift trends. Both proton and carbon chemical shifts ortho to the varying substituent follow the empirical parameter, Q. The ethylene carbon chemical shifts are proportional to those at the position para to the varying substituent.
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  • 41
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    Organic Magnetic Resonance 15 (1981), S. 319-320 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protonation of o-methoxy- and o-hydroxy-benzaldehydes in FSO3H—SbF5—SO2 solution was investigated by 1H NMR spectroscopy. The formation of the Z-carbonyl protonated molecule is explained by intramolecular hydrogen bonding.
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  • 42
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    Organic Magnetic Resonance 15 (1981), S. 324-325 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recently reported long-range deuterium isotope shifts of 13C NMR lines in [2-2H1]cyclodecanones are simply explained on the basis of changes in the averaging of otherwise equivalent conformations.
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  • 43
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    Organic Magnetic Resonance 15 (1981), S. 321-323 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isomeric tricyclo[4.4.1.12,5]dodecan-11-ols have been synthesized from the (6+4) cycloaddition product of tropone with cyclopentadiene. The configuration and conformation of each isomer was determined from the proton shift gradients induced in the olefinic proton signals in the 1H NMR spectra of intermediate compounds by Eu(fod)3.
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  • 44
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    Organic Magnetic Resonance 15 (1981) 
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  • 45
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    Organic Magnetic Resonance 15 (1981), S. 326-328 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton magnetic resonance spectra with natural abundance 13C satellites of p-chlorotoluene in isotropic as well as in oriented solvents are analyzed. The indirect C—H and H—H couplings are determined from the isotropic sample and one bond 13C isotope effects on the proton chemical shifts are measured. The direct couplings derived from the oriented samples are corrected for harmonic vibration and used to determine the molecular rα structure with a 6-fold hindering potential for the methl group. The resulting C—H and C—C bond lengths have errors which are smaller than 0.002Å. They deviate from the unsubstituted benzene molecule by between -1.1 and -0.5% for the C—H and between +0.3 and +0.5% for the C—C distances. It is not possible to obtain conclusive information about the hindering potential.
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  • 46
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    Organic Magnetic Resonance 15 (1981), S. 331-332 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C{1H} single frequency off-resonance decoupled spectra of secondary carbons with two chemically non-equivalent protons are analysed theoretically and experimentally. By a careful analysis of the frequencies of all six transitions all spectral parameters, including the geminal proton-proton coupling constant, can be determined very accurately.
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  • 47
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    Organic Magnetic Resonance 15 (1981), S. 329-330 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR spectra of two N-methylimidazole-substituted sterol esters are discussed. The calculated shifts are compared to those obtained experimentally. For one of the sterol esters the experimental and calculated data show good agreement, and the substituent increments can be evaluated. This does not apply in the case of the second sterol ester, where the steric and/or electronic effects of a further substituent - a hydroperoxy group in close proximity to the N-methylimidazole group - prohibits the additive calculation of substituent increments.
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  • 48
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    Organic Magnetic Resonance 15 (1981), S. 339-343 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemistry of various pairs of isomeric 2-cyclohexen-1-ylidenecyanoacetates was assigned using 1H NMR spectroscopy. The isomers with the γ-methylene or the γ-vinyl protons cis to the carbalkoxy group were found to have the signals of these protons at approximately 0.3 ppm and 1 ppm, respectively, downfield relative to their geometrical isomers or the corresponding 2-cyclohexen-1-ylidenemalononitriles. The observation regarding the γ-vinyl proton proved useful for the assignment of configuration to cyclohex-enylidenecyanoacetates derived form cholest-4-en-3-one. The large and constant downfield shift (c. 1 ppm) of the γ-vinyl proton when cis to the ester group results from the rigid cyclohexenylidenecyanoacetate system, in which the vinylic proton can approach more closely to the magnetically anisotropic ester carbonyl group.
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  • 49
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    Topics: Chemistry and Pharmacology
    Notes: Typically encountered proton-decoupled spectra of [U-13C]-labeled molecules or proton-coupled spectra of natural abundance or singly labeled molecules contain many nuclei which satisfy the weak coupling approximation. The spectra of such nuclei are frequently highly asymmetric and often appear to exhibit the skewed intensity distribution characteristic of strongly coupled spins. Analysis of typical cases indicates that such effects arise in the presence of at least one moderately strong coupling interaction in the spin system (Jδν ∼ 1/3), and the apparent intensity asymmetry reflects small differences in the spacing of unresolved components of the observed resonance. This effect is analogous to the case of ‘virtual coupling’ in which weakly coupled spins cannot be analyzed as first order spectra; however; the ABX spin system which generally serves as a model for such systems does not predict the existence of spectral asymmetry for the X resonances. Prediction of this asymmetry requires a spin system of at least four spins with at least ABMX complexity, and can be treated generally using the effective Hamiltonian approach of Poeple and Schaefer.
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  • 50
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    Organic Magnetic Resonance 15 (1981), S. 344-346 
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    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).
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  • 51
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    Topics: Chemistry and Pharmacology
    Notes: Rotation barriers around the metal - pyridine bond of various macrocyclic complexes of cobalt(III), rhodium(III), zinc(II) and magnesium(II) have been studied using the 13C longitudinal relaxation times, T1, of the carbon atoms of pyridine and the macrocycle. The data have been rationalized on the basis of steric and electronic factors. The influence of π back-donation on the rates of rotation around the axial Co—N and Rh—N bonds is discussed. The agreement found between the conclusions drawn from this study and X-ray data reported for complexes of identical or closely related structure demonstrates the validity of this method.
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  • 52
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    Organic Magnetic Resonance 15 (1981), S. 353-360 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proton chemical shifts correlate linearly with charges on hydrogen obtained by a method for iterative partial equalization of orbital electronegativity. The compounds studied comprise a wide variety of classes of molecules; all points fall on a single correlation line, showing the general importance of electronic effects in proton chemical shifts and the physical significance of the atomic charges. On the other hand, as there is no general correlation between charges on carbon and on hydrogen atoms, proton chemical shifts cannot be used as probes for charge densities on carbon atoms. Deviations from the correlation line can be attributed to anisotropy effects and provide an estimate for their magnitude.
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  • 53
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    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR signals of the two methyl groups in 4-hydroxy-1-isopropyl-2-oxaadamantane are anisochronous in the presence of Yb(fod)3. This is interpreted in terms of the different populations of three rotational conformers.
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  • 54
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    Organic Magnetic Resonance 15 (1981), S. 363-369 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H and 13C spectra of bicyclo[3.1.0]hexanes and thujanes have been recorded and assigned. Application of the Karplus equation has yielded dihedral angles, and a computer calculation of the angle of ring buckle as a function of the main dihedral angles has been carried out. The calculated angles of ring buckle agree well with known values in the bicyclo[3.1.0]hexanes, but for 1-methylbicyclo[3.1.0]hexanes and thujanes the results are not self consistent. It is suggested that the bridgehead substituent causes the boat to twist, although the twist can be reduced by an axial methyl substituent on C-4.
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  • 55
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nitrogen-14 nuclear quadrupole resonance (NQR) spectra of nicotinic acid derivatives, known as antitumor agents, are reported and analyzed in the framework of the Townes and Dailey theory. A strong correlation exists between the charge difference σNC - π at the pyridinic nitrogen and the inhibition of acetylcholinesterase by nicotinic acid derivatives, in which the inhibition potency (pI50) increases as the charge difference σNC - π increases. There are significant differences between 14N NQR spectra for the pyridinic nitrogen sites of nicotinic acid and nicotinamide; these can be explained in terms of the differences in hydrogen bond lengths.
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    Organic Magnetic Resonance 15 (1981), S. 375-389 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Computer programs for encoding canonical representations of stereochemical substructural environments are presented. Applications of these substructure codes in the study of relationships between molecular structure and chemical shifts observed in 13C NMR spectra are described, using natural products as examples. The utility of the codes for the detection of erroneous spectral assignment is illustrated.
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    Organic Magnetic Resonance 15 (1981), S. 390-393 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C NMR spectra of four types of azo coupling products from benzenediazonium chloride have been measured and interpreted, viz. hydrazo compounds with an intramolecular hydrogen bond (3-methyl-1-phenylpyrazole-4,5-dione 4-phenylhydrazone), azo compounds without an intramolecular hydrogen bond (4-hydroxyazobenzene), azo compounds with an intramolecular hydrogen bond (2-hydroxy-5-tert-butylazobenzene) and an equilibrium mixture of both the tautomers of 1-phenylazo-2-naphthol. The absolute values of the J(15N13C) coupling constants have been determined by recording the spectra of the 15N isotopomers, and have been used, in some cases, for 13C signal assignment. A relationship has been found between the chemical shifts of the C-1′ to C-4′ carbons of the phenyl group (from the benzenediazonium ion) or the 1J(15N13C) coupling constant, and the composition of the tautomeric mixture.
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    Topics: Chemistry and Pharmacology
    Notes: The conformational analysis of biologically active lofendazam (7-chloro-5-phenyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one) is carried out by means of lanthanide shift reagent assisted 1H NMR spectroscopy: the lanthanide induced shift computer simulation suggests that in deuteriochloroform the heterocyclic ring of lofendazam assumes a cycloheptene-like chair conformation, where 1-N moves away from trigonal stereochemistry to a very flattened pyramidal structure. At room temperature the conformational equilibrium is markedly shifted (85%) towards the conformer showing pseudoaxial H-1 and 5-Ph. The remarkable influence of steric requirements in controlling conformation, and the importance of 3- and/or 4-methyl groups in hindering the ring inversion at room temperature, have been verified by conformational analysis of suitable analogous 1,3,4,5-tetraydro-2H-1,5-benzodiazepin-2-ones.
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    Organic Magnetic Resonance 15 (1981), S. 399-400 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR signal assignment of a number of polyoxygenated triterpenes of the olean-12-ene and urs-12-ene series, carried out by considering the changes in chemical shift produced by the change of oxygenation pattern(s), and using methyl oleanolate as a model, are reported.
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  • 60
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    Topics: Chemistry and Pharmacology
    Notes: 33S NMR spectra have been obtained in the FT mode for some sulphones and sulphonic acids. The investigated compounds show narrow resonance lines. In the case of sulphones, the range of 33S chemical shifts is sufficiently wide, i.e. the effects due to changes in substituents are significant enough to allow further use of the 33S NMR of sulphones for quantitative analysis in petroleum chemistry.
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  • 61
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    Topics: Chemistry and Pharmacology
    Notes: One-bond C-α,H coupling constants are reported for glycine, alanine, sarcosine and related di- and tripeptides. A detailed study of the pH dependence of 1J(C-α,H) has led to a determination of additive increments, ζ, for the functional groups NH3, NHCO—, COO-, and CONH— which can be used, together with known values for NH2, COOH and alkyl substituents, to calculate 1J(C-α,H) in amino acids and peptides.
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  • 62
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    Organic Magnetic Resonance 16 (1981) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 63
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    Topics: Chemistry and Pharmacology
    Notes: The Bunte salt derivative was prepared from bovine insulin-A isolated from natural sources, and was purified by chromatography. Natural abundance 40.55 MHz 15N NMR spectra were measured in water and dimethyl sulphoxide. The latter solvent gave the best resolution, and 20 of the 22 possible amide nitrogen signals were detected. Several model oligopeptides were also measured and their usefulness for assignments is discussed.
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  • 64
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    Organic Magnetic Resonance 17 (1981), S. 97-102 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two-bond 13C—13C coupling constants are discussed on the basis of INDO-SCPT calculations. The dependence of 2J(CC) on bond angle variation and on methyl substitution is evaluated, and it is shown that 2J(CC) depends linearly on the bond orbital s-character product of the terminal carbon atoms, whereas no systematic relationship with the hybridization of the central carbon atom was obtained. Alkyl group substituent effects are found to be additive. The coupling constants of a number of cyclobutane derivatives are discussed on the basis of these structural relationships; it is shown that the experimental findings can be interpreted quite consistently by assuming a dual-pathway coupling mechanism.
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phosphorylation of the tetrapeptide Gly-Gly-His-Ala by phosphoamidate provides a model peptide for proteins which, in the course of their reaction, bind a phosphoryl group to an imidazole ring. 31P- and 1H-NMR data, including chemical shift and pK values, for this peptide and its three phospho-derivatives are presented. These data show that it is possible, by NMR studies, to decide whether or not a peptide or a protein is phosphorylated at the N-1 or at the N-3 position of an imidazole ring, and how this information can be achieved.
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  • 66
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    Organic Magnetic Resonance 16 (1981), S. 14-16 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 77Se chemical shifts of 79 mono- or disubstituted benzo[b]selenophenes are reported. The results in the 2- and 3-substituted derivatives closely parallel those previously obtained in the corresponding selenophenes. The measured parameters also correlate well with those measured in benzo[b]tellurophenes. The 125Te and 77Se chalcogen nuclei appear to be much more sensitive to substituent effects than the more classical nuclei. The effects of Cr(acac)3, Eu(dpm)3 and concentration on the 77Se NMR spectra are briefly discussed.
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  • 67
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    Organic Magnetic Resonance 17 (1981), S. 124-126 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of silver ion complexation on the 13C NMR of several rigid olefin structures has been determined. The silver ion induced chemical shifts (AgIS) are not amenable to easy interpretation. Addition of Yb(fod)3 forms binuclear Ag-Yb complexes with the olefin. Lanthanide induced shifts (LIS) fall off rationally with distance from the site of complexation and the averaged position of the lanthanide. The complexes may be used as probes of olefin stereochemistry.
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  • 68
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    Organic Magnetic Resonance 17 (1981), S. 110-117 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H and 13C NMR spectra of 2,3-disubstituted exo-5,6- and endo-5,6-bicyclo[2.2.2]octanes, and the corresponding alkanes, have been investigated to determine the effects exerted by an oxirane ring. The 1H NMR study showed that the anti protons, H-7a and H-8a, are significantly shielded and the syn protons, H-7s and H-8s, are deshielded, although to a smaller extent, by the exo-oxirane. An endo-oxirane has practically no effect on the same protons. The stereochemistry of epoxybicyclo[2.2.2]octanes is, thus, easily deduced from 1H NMR data. The 13C NMR study of the epoxy compounds provided an estimate of the value of α, β, γ syn and γ anti effects (to the epoxide oxygen) of an oxirane ring. In these rigid bicyclic molecules, of known geometry, the γ syn and the γ anti effects are of the same value, even though the dihedral angles are very different (0° and 120°).
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  • 69
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    Topics: Chemistry and Pharmacology
    Notes: 13C NMR shifts of 54 chalcones and their thiophene and furan analogues are analyzed by principal component analysis. Thus, a mathematical model is derived for the variation of the carbon shifts in each of seven classes. Two component models are found to be adequate by cross-validation. The first component corresponds to ordinary σpara values, while the second one differentiates benzenes, thiophenes and furans. This type of data analysis is a useful tool for checking the consistencies of spectral parameters. The model parameters, which describe systematic variations within each class, are also used for the study of substituent effects and discussed in relation to substituent constants in linear free energy relationships.
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  • 70
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    Topics: Chemistry and Pharmacology
    Notes: 15N Chemical shifts of cis-decahydroquinoline, N-methyl-cis-decahydroquinoline, and of 19 methyl substituted NH- and NCH3-cis-decahydroquinolines are reported. Shift values of conformationally homogeneous compounds can be used to determine the chemical shifts of the possible conformations of the mobile compounds. Equilibrium constants derived from the shifts of the contributing conformations agree with results of low temperature 13C NMR spectroscopy.
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  • 71
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    Organic Magnetic Resonance 17 (1981), S. 131-133 
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    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.
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  • 72
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    Organic Magnetic Resonance 16 (1981), S. 47-51 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR spectra of β-methyl-β-nitrostyrene and its nine mono- and dimethoxy-derivatives have been determined. Chemical shift data are presented and analysed in a self-consistent manner which allows most of the signals to be unambiguously assigned. Trends in the data can be interpreted in terms of the conformational properties of the variously-substituted compounds.
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  • 73
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    Topics: Chemistry and Pharmacology
    Notes: N,N-diisopropylamides and -thioamides show hindered rotation around the N—CH bonds, and the presence of mixtures of conformational isomers can be demonstrated at temperatures below 273 K in solution. 1H and 13C NMR spectra of these conformers are measured and assigned. The 13C data serve to study through-space effects on 13C chemical shifts, which strongly depend on the conformations of the isopropyl groups. For amides, a through-space shielding of the N-methine carbons is found to exist only for conformers in which the methine hydrogen atom is spatially close to the oxygen atom. Chemical shift differences between amides and thioamides can be rationalized in terms of through-bond and through-space contributions, and serve for a better understanding of the shift differences in N,N-dialkylamides and -thioamides.
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  • 74
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    Organic Magnetic Resonance 16 (1981), S. 52-56 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 15N and 13C chemical shifts and the 1J(15N15N), 1J(15N13C) and 1J(13CH) coupling constants have been determined for a number of 15N-enriched cyclic and acyclic secondary nitramines. The results are interpreted in terms of both electronegativity effects and conformational factors.
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  • 75
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    Organic Magnetic Resonance 16 (1981), S. 57-59 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High precision 14N screening measurements are presented for some nitroalkanes. The screening increases as the dielectric constant of the solvent decreases in all cases considered. The β effect on the nitrogen screening is found to be largely independent of solvent, and is thus an intrinsic property of the nitroalkanes. Good agreement is obtained between the observed solvent effects on nitrogen screening and those calculated by the SOS procedure using INDO/S parameters. It is concluded that the measured nitrogen screening changes monitor the electronic changes which occur in the nitroalkanes as the medium is changed.
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  • 76
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    Organic Magnetic Resonance 16 (1981), S. 60-62 
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    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.
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  • 77
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    Organic Magnetic Resonance 17 (1981) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 78
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    Organic Magnetic Resonance 17 (1981), S. 157-162 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C data of several new amino protecting groups of the urethane structure are reported. The speeds of acidolytic cleavage are correlated with the 13C parameters.
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  • 79
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    Organic Magnetic Resonance 16 (1981), S. 65-67 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR spectral studies of tembamide (1) and aegeline (2), constituents of Fagara hyemalis and Aegle marmelos respectively, and a series of their structurally related amides (3-13) have been carried out. The assignment of the resonances of two related dimers are also reported. The assignment of the various resonances were made by considering the changes in chemical shifts produced by the change of substituents and also by using 1, 13 and a related compound as model compounds.
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    Organic Magnetic Resonance 16 (1981), S. 68-70 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: Several methyltetrahydrofurans have been studied in HSO3F—SbF5—SO2 solution. O-Protonation was observed from 1H NMR measurements at low temperature, and the coupling constants between +OH and the CH protons α to oxygen were measured from the CH signals. A conformational interpretation could be carried out from these results.
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  • 81
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    Organic Magnetic Resonance 16 (1981), S. 71-72 
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    Topics: Chemistry and Pharmacology
    Notes: Eight alkylcyclopropane derivatives were prepared in a conventional manner and analysed by 13C NMR spectroscopy. Additivity parameters were calculated from the chemical shifts of the endocyclic carbons, and the configurational structures derived for these compounds are confirmed by the internal coherence found for this set of parameters.
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  • 82
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    Organic Magnetic Resonance 16 (1981), S. 73-74 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: A comparative study of the 13C spectra of 13 1-pyrazolines is reported. The results show that the chemical shifts of some carbons are very sensitive to the relative positions of substituents on the 3,4 and 4,5 bonds.
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    Organic Magnetic Resonance 16 (1981) 
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  • 84
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    Organic Magnetic Resonance 16 (1981), S. 75-77 
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    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 NMR signal assignments of the labdane diterpenoids andrographolide and 14-deoxyandrographolide, along with their acetates, and isodeoxyandrographolide have been made. This study indicates that the C-6 and C-11 resonance assignments of isovirescenol-B, made earlier, should be interchanged.
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    Organic Magnetic Resonance 16 (1981), S. 82-84 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: A study of the correlation of solvent effects on the chemical shifts of the methyl protons of sylvan, toluene and α-picoline led to the conclusion that the preferential site of solvation of the furan ring in acidic solvents is the π-electron cloud and not the n-electron orbital of the oxygen atom.
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    Organic Magnetic Resonance 17 (1981), S. 180-181 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    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.
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    Organic Magnetic Resonance 17 (1981), S. 182-185 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: The selective population transfer method has been applied to the study of a secondary amide and of the corresponding iminium salt. Important signal-to-noise enhancements were accessible in both fully coupled and proton decoupled 15N and 13C spectra. Moreover, the resolving power of the method was exploited for the accurate determination of long range 15N1H coupling constants. Experiments in which the selective inversion of transitions pertaining to the 15N satellite spectrum of multiplets which themselves constitute the 13C satellite spectrum of the main proton resonances could be carried out. The influence of a change from the amide to the iminium structure on the magnitudes and the signs of various 15N1H and 15N13C coupling constants is discussed.
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  • 88
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    Organic Magnetic Resonance 17 (1981), S. 186-190 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton NMR spectra of 14 actinomycins and the 13C NMR data for four of these compounds were compared with those of actinomycin D. These compounds differ from actinmycin D by the replacement of one or both proline residues by sarcosine, azetidine-2-carboxylic acid, 4-ketoproline, or cis or trans isomers of 4-hydroxy-, 4-chloro- or 4-methylproline. In those (aniso) compounds in which one proline residue is replaced, the possibility of isomerism was considered, since replacement could be located in either the α- or β-peptide. Except for the sarcosine case, for which both isomers have been isolated, the aniso-actinomycins gave spectra in which the presence of a second isomer was undetectable. Attempts to utilize the NMR data to determine which peptide contained proline, and which its congener, produced the tentative conclusion that in these compounds there is a biosynthetic preference for replacement of the β-peptide proline residue. In comparing conformationally dependent NMR parameters for the various actinomycins, the most obvious variations appeared in the proline congener α-proton splittings. Some of these (for cis isomers of 4-chloroproline and 4-methylproline) reflected different pyrrolidine ring geometries to that of proline, while others (for the corresponding trans isomers) did not. Only minor differences were apparent in the conformations of other regions of the peptide moieties.
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  • 89
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    Topics: Chemistry and Pharmacology
    Notes: 14N Nuclear quadrupole resonance (NQR) spectra of several N-acetyl amino acids and related compounds are reported and analyzed within the framework of the Townes and Dailey theory. The inductive effect of the chloroacetyl group on the nitrogen is discussed. A positive correlation between the π-σNC electron density at the nitrogen and the Taft inductive parameter σ* is observed, suggesting that the nitrogen π-charge density in the N-acetyl amino acids does not vary appreciably. NQR data for hippuric acid are compared to the 14N quadrupole parameters extracted from ENDOR data reported for X-irradiated hippuric acid.
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  • 90
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    Notes: Nitrogen-14 nuclear quadrupole resonance frequencies at 77 K are reported for a series of carbazole compounds including N-vinylcarbazole. Differences in charge distribution between pyrrole and carbazole are explained on the basis of delocalization of pi electrons. Effects of the aldehyde and vinyl groups on charge distribution are discussed. Sigma bond polarization between the pyrrole nitrogen and the nitroso nitrogen toward the pyrrole nitrogen exists in N-nitrosocarbazole.
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  • 91
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    Topics: Chemistry and Pharmacology
    Notes: The boric acid-catechol system in aqueous solutions has been studied by means of 11B, 1H and 13C NMR over wide ranges of concentration and pH. 11B spectra show a striking difference between the complexation possibilities of dilute and more concentrated solutions of boric acid. Both the 1:1 and 1:2 complexes can be simultaneously observed by 13C NMR.
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  • 92
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    Topics: Chemistry and Pharmacology
    Notes: The methylene protons of the ethyl ester function at C-2 in triethyl meso, cis-1,3-dimethylcyclohexane-1,2,3-tricarboxylate (A) are anisochronous, despite the apparent symmetry of structure A. The necessary diastereotopy is thought to be engendered by the central ester being stabilized in a rotamerization in which the O:C·O plane is held parallel to the general plane of the 6-membered ring while fast exchanges take place among rotamers about the alkyl-oxygen bond; other rotamers about the ester axis are thought to encounter high order repulsive steric/polar interactions with the flanking ester functions and C-methyl groups. Evidence for the axial orientation of the C-1 and C-2 ester functions in A, based on comparisons of its 1H NMR spectral characteristics with those of its RS-cis, trans and meso, trans analogues, is presented. The role of ion-pairing in the stereoselectivity of methylation of precursor enolates, leading to the formation of these three systems, is briefly discussed. A comment on the appropriateness, or otherwise, of drawing conformational conclusions from the magnitudes of the anisochrony in comparable systems is included. Triester A is thought to be the first instance where atropisomerism about an sp3—sp2 bond involving an ordinary ester function has been detected employing a prochiral sensor group.
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    Organic Magnetic Resonance 16 (1981), S. 239-241 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of the intermediate obtained in the come of the nitrationof 2-furancarboxaldehyde was investigated by means of 1H and 13C NMR. It was shown unambiguously that this intermediate is 2-acetoxy-2-diacetogymethyl-5-nitro-2,5-dihydrofuran.
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    Organic Magnetic Resonance 16 (1981), S. 242-244 
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    Topics: Chemistry and Pharmacology
    Notes: The analysis of the 13C FT NMR spectra of 2-hetera[3](1,1′)ferrocenophanes containing an oxygen, sulphur, selenium atom, phenyl-substituted nitrogen or a methylene group in the 2-position of the bridge has been carried out. The electronegativity of this fragment affects both chemical shifts and coupling constants, but no simple relationship was found.
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    Organic Magnetic Resonance 16 (1981), S. 245-246 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: The ENDOR spectrum was obtained for the benzo[c]cinnoline anion radicalin 1,2-dimethoxyethane. The hfs constants of the protons correspond with those found by EPR spectroscopy, and also agree well with the qualitative tendency of the reported spin density distributions by HMO calculation.
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    Organic Magnetic Resonance 16 (1981), S. 247-249 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental solvent effects on 13C and 17O chemical shifts of acetone, and 13C chemical shifts of acetonitrile are compared with theoretical calculations by Jallali-Heravi and Webb (solvaton model). Calculated values are, generally, in agreement with experimental results for atoms belonging to polar groups, but not for methyl carbons for which van der Waals interaction effects are predominant.
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    Organic Magnetic Resonance 16 (1981), S. i 
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    Topics: Chemistry and Pharmacology
    Notes: Erratum.
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    Organic Magnetic Resonance 16 (1981) 
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    Organic Magnetic Resonance 16 (1981), S. 261-265 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: The preferred conformation of 8-methyl-cis-thiahydrindane has been both estimated by 13C NMR chemical shifts and determined by low temperature 13C NMR spectroscopy to be the conformer with the methyl group equatorial with respect to the cyclohexane ring. This result is in disagreement with the interpretation of the temperature dependence of the CD spectra of (+) and (-) 8-methyl-cis-2-thiahydrindane, whereby the conformation with the methyl group axial with respect to the cyclohexane ring was claimed to be the preferred conformation. The preferred conformation of the related oxygen heterocycle, 8-methyl-cis-2-oxahydrindane, has been estimated by 13C NMR chemical shifts to be the conformer with the methyl group axial with respect to the cyclohexane ring. Possible reasons for these observations are discussed.
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR spectra of 48 polychlorobromoalkanes have been studied. Unlike the 13C signals of chlorine-containing groups (38-105 ppm), those of bromine-containing fragments, with the exception of CBr2 (60-70 ppm), appear in a rather narrow range (25-50 ppm) and are shifted to higher field in relation to similar chlorine-containing groups. The spin-spin coupling constants in similar bromine- and chlorine-containing groups practically coinciEN. Calculation of the chemical shifts for the polyhaloalkanes under study according to the additivity scheme, as previously observed for polychloroalkanes, renders values which are in considerable discord with experimental values (up to -32 ppm for CBr3). These discrepancies may be compensated for by corrections for the binary interaction of halogen atoms by grouping the halogen-containing fragments according to the geminal, vicinal, 1,3-, 1,3,5- and 1,2,3-arrangement of halogen atoms, and by introducing an increment for the position of the halogen at the secondary atom. It is established that as compared to 1-monohaloalkanes: (a) in the case of the geminal arrangement of halogen atoms the α- and γ-effects diminish (Δ α from -3.2 to -8 ppm; Δγ = 2.6 ppm), while the β-effect increases slightly (from 0 to 1.2 ppm); (b) in the case of a vicinal arrangement both the α- and β-effects diminish (by about -3.5 ppm) and the γ-effect remains constant, as if the vicinal system of the halogens was topologically insulated; (c) for the 1,3- and 1,3,5-arrangement of halogens their mutual influence is weak (about -0.5 ppm for each halogen atom in the α- and γ-positions); (d) the 1,2,3 system (serial arrangement of halogen atoms) is the sum of two vicinal fragments and hardly deviates from the additivity scheme; (e) the arrangement of a halogen at the secondary C atom enhances the α-effect (Δα = 2.8 and 1.0 for methyl and methylene, respectively, in the case of Cl, and 3.5 and 3.7 ppm in the case of Br); the variation of the β-effect has a different sign in relation to CH3 and CH2 groups (+1.2 and -1.7 for Cl, and +2.5 and -1.0 for Br). More distant effects of halogens (δ and ∊) were not considered. The determined increments (Δα, Δβ and Δγ) for the α-, β- and γ-effects of chlorine and bromine atoms allow the prediction of the 13C chemical shifts in polyhaloalkanes with an accuracy up to ±1.5 ppm. Some deviations of up to ±5 ppm may be connected with the influence of a three particle interaction of halogen atoms, which was taken into account only in the case of a geminal arrangement of halogen atoms.
    Additional Material: 4 Ill.
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