摘要:

AbstractThe1H and13C NMR spectra of 22 pinane derivatives have been recorded and completely assigned. The spectral data for this set of compounds provide information about the conformation of these molecules and allow the deduction of the various structural effects observed in the bicyclo[3.1.1]heptane series.

ISSN:0749-1581    

DOI:10.1002/mrc.1260300902

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractVicinal13C,1H coupling constants were used to establish the configuration of a 3,5‐disubstituted notricyclene. The assignment procedure is supported by independent measurements of13C,2H coupling constants in 3‐ deuterionortricyclene and confirmed by1H,1H NOE data forexo‐3‐N‐acetylamino‐exo‐5‐pivalo

ISSN:0749-1581    

DOI:10.1002/mrc.1260300903

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractKnown selective 2D J‐resolved methods for the determination of long‐range proton–carbon coupling constants,nJ(C, H), have been modified and improved by introducing an INEPT or refocused INEPT sequence as a preparation period in the Bax–Freeman selective spin–flip method, or using exclusively selective pulses from the decoupler channel in the selective INEPT‐2D experiment. The greater sensitivity achieved allowed the determination of these couplings, even for quaternary carbons, in a short acquisition time and with excellent reproducibility forc

ISSN:0749-1581    

DOI:10.1002/mrc.1260300904

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractProton NMR spectra suggest that the conformation withtransvicinal hydrogens is favored for ephedrine as the free base in deuterium oxide, although in non‐polar solvents, such as deuteriotrichloromethane, thegauchevicinal hydrogen conformations are favored, as has been reported previously. The conjugate acid has primarilygauchehydrogens. In contrast, thetrans‐hydrogen rotamers of pseudoephedrine dominate for both the non‐protonated and protonated forms in deuterium oxide. Hydrogen bonding is unlikely to be as important as usually assumed in determining the conformational preferences of these subst

ISSN:0749-1581    

DOI:10.1002/mrc.1260300905

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractAb initioNMR shieldings, based on the Hansen and Bouman theory, were calculated for some polyene compounds in order to apply the method to retinal proteins. It is shown that theab initioresults reproduce well the magnetic properties peculiar to the polyene13C chemical shifts. In addition, the13C and15N shieldings were calculated for several amines as model compounds of the retinal moiety located in bacteriorhodopsin, and the effect on the chemical shifts of thesyn–antiorientation about the CN double bond and the protonation of the Schiff base was investiga

ISSN:0749-1581    

DOI:10.1002/mrc.1260300906

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract17O NMR was used to probe the steric and electronic substituent effects in furan‐2,3‐dione derivatives. The carbonyl17O chemical shifts correlate with Hammett constants and IR carbonyl stretching band frequencies for 5‐(para‐substituted‐phenyl)furan

ISSN:0749-1581    

DOI:10.1002/mrc.1260300907

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe1H NMR spectra (300 MHz) of the aminoglycoside antibiotics apramycin and sisomicin (free bases) were completely analysed by 1D and 2D methods (mainly1H1H and1H13C shift‐correlation spectroscopy). The complete1H nd13C NMR assignment of a series of semisyntheticN‐polyacetyl‐ andN,O‐polyacetyl derivatives of kanamycins A and B, tobramycin, apramycin and sisomicin was also achieved via these techniques. The effect of acetylation on the1H and13C chemical shifts,1H1H coupling constants and ring conformations is discussed. The vicinal coupling constants for the unsaturated ring in sisomicin, calculated on the basis of the energetically favoured conformation predicated by the MMP2 method, are in good agreement with the expe

ISSN:0749-1581    

DOI:10.1002/mrc.1260300908

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractTitanium‐based Ziegler–Natta catalysts for the polymerization of buta‐1,3‐diene give linear trimers of butadiene among other by‐products. A combination of1H and13C NMR, DEPT and 2D‐INADEQUATE gives exhaustive assignments of their13C NMR spectra and affords their structures. All these trimers are dodeca‐2,4,6,10‐tetraenes which have an isolatedcisdouble bond. The internal double bond of the conjugated triad has atransconfiguration in each isomer, and the trimers differ only in the outer double bonds. The13C NMR spectra of the timers reveal that the signal position of the carbon involved in the conjugated double bond series is mainly controlled by the configuration of the adjacent double bond and, to a lesser extent, by the geometry of its own double bond. The oligomers studied serve as models for polyacetylene. Some reassignments in the spectra of oligomers of terminal acetylen

ISSN:0749-1581    

DOI:10.1002/mrc.1260300909

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe NMR resonance frequency ratio of the31P NMR resonance shift standard 85% orthophosphoric acid (H3PO4) and the1H standard tetramethylsilane (TMS) was determined by means of the ‘dispersed phase’ method. The Ξ value, equal to 108times the resonance frequency ratio, was 40480737.0 ± 0.2 Hz at 25°C. A small dependence on temperature (−0.11 Hz °C−1) and on phosphoric acid concentration (−0.50 Hz %−1) was observed around 25°C. Traces of iron in phosphoric acid were found to have a negligible effect on Ξ values, although line widths increased. The determination of Ξ allows accurate referencing of31P NMR spectra relative to the1H resonance of internal TMS or of a secondary1H shift standard. The accuracy of the31P NMR resonance shift scale is primarily limited by the uncertainty of solvent‐induced1H res

ISSN:0749-1581    

DOI:10.1002/mrc.1260300910

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractA heteronuclear multiple quantum correlation (HMQC) experiment was used to correlate the6Li and15N chemical shifts of mixed aggregates of [6Li,15N]lithium 2,2,6,6‐tetramethylpiperidide with [6Li]LiBr, [6Li]LiCl, and [6Li]lithium cyclohexenolate. Optimization of the experiment to spin systems containing more than one weak spin is discussed. The two‐dimensional correlations represent a substantial improvement in sensitivity and resolution relative to one‐dimensional me

ISSN:0749-1581    

DOI:10.1002/mrc.1260300911

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY