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  • 1
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 5 (1973), S. 403-406 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spin information should be passed most effectively from a carbon-hydrogen bond to the p-rich carbon-carbon bond of an adjacent cyclopropane ring when the two bonds are parallel. The existence of such a mechanism is tested in a series of spiro hydrocarbons and epoxides in which four-bond zigzag (W) couplings are absent. The structure is varied from the ideal parallel-orbital geometry of spirohexane and the homologous epoxide to the unfavorable staggered-orbital geometry of spiro[2·5]octane and its epoxide. In the parallel-orbital situation, a four-bond non-W coupling of about 0·2 Hz is found; this coupling is absent in the other geometric situations. The meager ability of the cyclopropyl bonds to pass spin information, when compared to the π-orbitals in alkenes, is discussed in terms of the electronic structure of cyclopropanes.
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  • 2
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational preference of the thymine base ring with respect to the sugar ring in β,β,β,-trichloroethyl 5′amino-5′-deoxythymidine-5′-phosphate has been studied by 13C n.m.r. spectroscopy. The magnitude of the three bond vicinal coupling constant, J(C-2, H-1′), for β,β,β-trichloroethyl 5′-amino-5′-deoxythymidine-5′-phosphate and the similarity between the chemical shifts for the furanose carbons C-1′, C-2′, and C-3′ in β,β,β-trichloroethyl 5-′-amino-5′-deoxythymidine-5′-phosphate and in β,β,β-trichloroethyl thymidine 5′-phosphate indicate that the amino analogue exists in aqueous solution predominantly in the anti conformation, as is the case with natural nucleotides.
    Additional Material: 1 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 21 (1983), S. 539-543 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new bicyclic system, 3,7-diazabicyclo[4.1.0]heptane, has been prepared from 3-(ethoxycarbonyl)-7,3-oxazabicyclo[4.1.0]heptane by reaction with sodium azide and reduction of the resulting tosyloxy azide with lithium aluminum hydride. The molecule can exist in four stereoisomeric half-chairs, depending on the configuration of the two nitrogen atoms. Half-chair ring reversal and piperidine nitrogen inversion are fast on the NMR time scale at all observed temperatures. Inversion of the secondary aziridine nitrogen becomes slow as the temperature is lowered (Tc= -10°C). Complete analysis of the 1H spectrum was possible with the 1,5,5-trideuteriated analog. At slow exchange, two aziridine invertomers are present with an exo/endo ratio of approximately 0.7 in toluene-d8, 0.7 in CH2Cl2 and 1.7 in CHCl3/CH2Cl2. The free energy of activation for nitrogen inversion is 13.2 kcal mol-1 at -10°C in CHCl3/CH2Cl2.
    Additional Material: 2 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 22 (1984), S. 613-615 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperatuure dependence of the vicinal OCH2CH2 coupling constant in the six-membered ring δ-valerolactone suggests the presence of at least two conformers of unequal energy. Analysis of this temperature dependence by the Wood-Fickett-Kirkwood method in six solvents produces free energy differences in the narrow range 0.8-1.4 kcal mol-1, with a mean of 1.0 kcal mol-1 and no apparent dependence on solvent polarity. Thus the two conformers, probably the half-chair and the classic boat, have similar polarities. The analogous four- and five-membered lactones show little or no temperature dependence for their analogous coupling constants, in agreement with the presence of a single conformation for these rings.
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 22 (1984), S. 301-307 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dipolar relaxation of 15N in anilines and anilinium ions is influenced by overall motion of the molecule, by rotation about the aryl--nitrogen bond, by inversion of the aniline nitrogen and by interactions of the NH2 or NH3+ group with the solvent. These factors are assessed by comparison of the 13C and 15N dipolar relaxation times as a function of para-substitution on the aryl ring. In the anilines (solvent CDCl3), electron withdrawal brings about faster relative motion of the amine side-chain, contrary to expectation from consideration of C—N rotation but in agreement with the effects from nitrogen inversion. The 15N dipolar relaxation time correlates with the Hammett σp. For the anilinium ions (solvent Me2SO-d6), there is no correlation with σp and no qualitative relationship with either C—N rotation or N inversion. Nitrogen-15 relaxation, corrected for overall motion as judged by ring 13C relaxation, correlates with the inductive parameter σI. Electron withdrawal through induction reduces hydrogen bonding and increases side-chain mobility. For most of the anilines and for all of the anilinium ions, solvent interactions cause the nitrogen side-chain to be less mobile than the aryl ring. Under these circumstances, the Woessner approach cannot be used to calculate barriers. The hydrogen bond donor properties of the anilines are reduced in the absence of electron-donating substituents, and the first barriers to NH2 rotation/inversion were calculated by this procedure: aniline in CDCl3 3.5 kcal/mol, p-chloroaniline in CDCl3 3.4 kcal/mol and p-nitroaniline in acetone 3.8 kcal/mol.
    Additional Material: 5 Tab.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 1 (1969), S. 345-349 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to determine the effect of a single methyl group on the chemical shifts of protons in a cyclohexane ring, methylcyclohexane-1,2,3,3,5,5,-d6 has been synthesized. The protons in the 4-position and the 2,6-equatorial protons are not significantly different from those in ring-frozen cyclohexane. The 2,6-axial protons, however, experience an up-field shift of about 15 Hz from the position of the other axial protons. These observations are discussed in terms of the structure of methylcyclohexane.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 3 (1971), S. 389-403 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The NMR spectra of the nonaromatic protons in several benzo-substituted five- and six-membered rings have been analyzed at 60- and 90-MHz. The vicinal coupling constants from the—CH2—CH2—fragments give a quantitative assessment of the degree of ring flattening. The distortions are discussed in terms of the structural components of the molecules.
    Additional Material: 8 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 7 (1975), S. 266-273 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The proton magnetic resonance spectra of catechol, epinephrine, dopamine, synephrine, tyramine and amphetamine have been analysed by computer simulation. The chemical shifts and coupling constants are discussed, with their molecular implications. Convenient parameters are introduced for the additivity of substituent effects on chemical shifts of aromatic protons. The additivity rule of coupling constants is extended to these compounds.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 9 (1977), S. 621-626 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various arithmetic combinations of Jtrans and Jcis from the AA′BB′ analysis of —CH2 - CH2- fragments in 6-membered rings have been examined for their relationship to the internal torsional angle Ψ. The simple ratio R (Jtrans/Jcis) appears to offer the most complete removal of substituent electronegativity effects and hence the best values of Ψ. The Karplus equation is very inaccurate when the substituents are highly polar. The simple difference D (Jtrans-Jcis) overcompensates for electronegativity effects and thus also gives relatively inaccurate torsional angles. An alternative, artificial linear combination of the coupling constants, such as D′ (Jtrans-2Jcis), appears to be able to provide torsional angles that are almost as good as those from the R value, although the Karplus A value must be evaluated. Adjustment of the simple difference D for electronegativity is possible by including a function of the AA′ and BB′ chemical shifts. These results are fairly good, and the parameter A need not be evaluated. This approach may fail, however, with particularly anisotropic substituents, since the chemical shift may depend on factors other than electronegativity. Although all five methods give reasonably good results, the R value appears to offer the most reliable results for the full range of substituents.
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 265-269 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The γ effects on 13C shielding have been examined for a series of rigid molecules containing the substituents CH3, OH, NH2, F, Cl, Br or I. Plots of the γ effect vs the C—C-α—C-β—X dihedral angle are well scattered if the plots do not distinguish modes of substitution. For the series in which the resonating carbon is CH2, however, fairly linear correlations are observed for X=CH3, OH, NH2, Cl and Br. It is concluded that within a structurally defined and substitutionally homogeneous series, there is a reasonably linear stereochemical dependence. Although substitution at C-α does not seriously alter the linear relationship, hybridization of the intermediate carbons may be important. The slopes of the plots for the γ effect vs dihedral angle are remarkably similar. Neither a strictly steric (van der Waals) nor a strictly polar source can be the cause of the linear relationship, since our series of substituents ranges widely with respect to both size and electronegativity. The only two factors that are constant within the series are the removal of the hydrogen atom (C—C—C—H to C—C—C—X) and the addition of the bonding and nonbonding orbitals on X that were not present on H.
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