Der Einfluß von Hydroxylgruppen auf die Größe der13C,13C-Kopplungskonstanten

The¹³C,¹³C coupling constants of some alcohols with different structures were determined and the influence of hydroxyl groups on the magnitude of the coupling constants was evaluated by comparison of the data with the values obtained for the corresponding hydrocarbons. It is shown, that the introduction of a hydroxyl group in an organic molecule leads to an increase of the¹ J (CC) coupling constant of about 3 Hz.     

Fulvene,VII. Analyse der 13C- und 1H-NMR.-Spektren

Carbon-13 and proton NMR. spectra of pentafulvene and of a series of 6-substituted fulvenes have been analysed and assigned by homo- and heteronuclear double resonance and with the aid of iterative computation. ¹³C and ¹H chemical shifts are interpreted in terms of substituent effects and compared with π-electron charges calculated for the unsubstituted fulvene. From ¹³C shifts a 10 percent contribution of dipolar structures to the electronic configuration of fulvene may be estimated. All long-range proton-proton coupling constants including relative signs and some proton-carbon couplings in the fulvene spin system have been determined and assigned.     

Die Abh?ngigkeit von CC-Bindungsl?ngen von Hybridisierung und Konjugation

Ohne Zusammenfassung

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Dependence of CC bond lengths on hybridization and conjugation

     

13C-, 14N- und 1H-kernresonanzspektroskopische Untersuchungen an m-/p-substuierten N-Methylpyridiniumjodiden

In a series of 21 m-/p-substituted N-methylpyridinium salts, N-methyl proton, carbon-13 and pyridinium nitrogen-14 chemical shifts were determined by heteronuclear double resonance, and partly in the case of the ¹⁴N nucleus and the methyl protons by direct measurement. In a few compounds the quadrupole relaxation times proved to be too short for the ¹⁴N coupling to be detected. This problem was overcome by adequately rising the sample temperature. For all three nuclei a marked dependence of the chemical shifts on the nature of the substituent could be established. Increased nitrogen π-electron density shifts the resonances towards higher fields. In the case of the ¹⁴N shieldings, this tendency is attributed to changes in the paramagnetic screening term, whereas for ¹³C and ¹H an interpretation is given in terms of a neighbour anisotropy contribution. The latter explanation is based on the observation that the calculated carbon and hydrogen charge densities show no significant variations throughout the series. Excellent shift correlations were obtained with Hammett substituent constants when σ⁺-values were used for donor substituents. A similar substituents, dependence could be observed for the direct ¹³CH methyl coupling constants, whose magnitude increases with decreasing nitrogen charge density.     

13C-13C NOESY: an attractive alternative for studying large macromolecules

13C direct detection provides a valuable alternative to 1H detection to overcome fast relaxation because of its smaller magnetic moment. 13C-13C NOESY spectra were acquired for a dimeric protein of molecular mass 32 000 and for a monomeric analogue. With increasing molecular mass, the quality of 13C-13C NOESY spectra improves while the scalar-based experiments become less sensitive, as predicted by the increase in the molecular mass. 13C-13C NOESY spectra of the dimer were acquired with different mixing times. The mixing time can be tuned to detect mainly one-bond correlations, or it can be increased to also detect correlations between nuclei at longer distances. It is proposed that 13C-13C dipolar-based experiments provide a promising tool for signal detection and assignment in large macromolecules, such as multimeric species and macromolecular complexes, for which scalar-based experiments become less effective.     

C-13 NMR-spektroskopische Untersuchung von Jodthiophenen

The carbon-13 NMR data of all possible isomeric iodo-substituted thiophenes are discussed.

     

13C-13C spin-spin coupling constants in 3-carene

Novosibirsk Institute of Organic Chemistry, Siberian Branch, USSR Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, Vol. 6, pp. 853–854, November–December, 1989.