摘要:

AbstractThe15N NMR spectra of fiveN‐(o‐aminophenyl)‐N′ substituted ureas and their hydrochloride salts were recorded in DMSO. N‐1 was more shielded in these ureas than inN‐phenyl‐N′‐methylurea. The shifts of N‐3 varied with the substituents. Proton exchanges at N‐3 were observed when the spectra of the hydrochloride salts were recorded. The preferentialtrans‐transorientation of the protons with respect to the carbonyl in the ureido group was confirmed by NOE difference spectroscopy. In the solid, the conformation ofN(o‐aminophenyl)‐N′‐methylurea, which was determined by x‐ray diffraction, was found to be similar to the suggested conformation in solution; the15N shifts of this compound in the solid state were determined by15N cross‐po

ISSN:0749-1581    

DOI:10.1002/mrc.1260300702

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractTriterpenes with the protostane skeleton, which are available from biomimetic rearrangements of lanostane derivatives, were analysed by one‐ and two‐dimensional high‐field1H and13C NMR spectroscopy. Complete assignments of the proton and carbon signals of 11α‐acetoxy‐3β‐benzoyloxy‐5α.9β‐protost‐13(17)‐ene (4) and of 11α‐acetoxy‐31‐nor‐5α,9β‐protost‐13(17)‐en‐3‐one (5) are presented. The assignments were largely determined using substituent chemical shift and conformational effects and by a combination of DEPT,1H‐‐1H COSY,1H‐‐13C HETCOR and XCORFE spectra. Nuclear Overhauser effect and lanthanide‐induced shift experiments were also useful for assignments. The results confirm the structure of 4 proposed previously on the basis of the low‐resolution spectra, and provide evidence for the structure of the new fusidane 5. The effect of methyl substitution at the 4β‐position on the13C chemical shifts is briefly discussed. The assignment of the sp2carbon atom signals reported for diacholest‐

ISSN:0749-1581    

DOI:10.1002/mrc.1260300703

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThree different experimental techniques are compared to find the most efficient protocol for 2D13C,31P correlation spectroscopy. It is shown that the best signal‐to‐noise ratio is given by the polarization transfer experiment for31P detection and by the HMQC experiment for13C detection. Applications of these techniques for13C,31P correlation of β‐nicotinamide adenine dinucleotide (NAD+) and a mixture of three different mononucleotides are des

ISSN:0749-1581    

DOI:10.1002/mrc.1260300704

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractF1region‐selected variants of the HMBC experiment were compared and evaluated. In particular, a significant advantage was demonstrated for an E‐BURP‐2 pulse over a Gaussian 270° pulse for region‐selected applications. The Gaussian 270° pulse would still, however, be the preferred pulse for use in single‐resonance, on‐resonance selective excitation. Data are presented from NMR spectrometers both equipped and not equipped with programmable pulse modulators (waveform generators). Pulse evaluations were performed using the simple heteroaromatic alkaloid quindoline; application of the technique to the important immunosuppressive cyclic peptide cyclosporin‐A is also presente

ISSN:0749-1581    

DOI:10.1002/mrc.1260300705

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractVariable‐temperature13C CP/MAS NMR experiments were carried out on crystalline (±)‐3,4‐di‐O‐acetyl‐1,2,5,6‐tetra‐O‐benzyl‐myo‐inositol. Three distinct phases can be distinguished from their NMR characteristics, each stable over a well defined temperature range, in accord with previous calorimetric studies. The differences between the spectra of the distinct phases suggest that structural variations between them are small. At least two of the aromatic ring moieties of the molecule were shown to be experiencing motional averaging in each of the three phases. Transitions between the phases, monitored by following changes in the NMR spectra, exhibited significant hysteresis but showed no evidence for pre‐organizational behaviour in the form of intermediate species. These results are discussed in the context of the unusual ‘jumping’ motion of the crystals associated with passage through the phase I

ISSN:0749-1581    

DOI:10.1002/mrc.1260300706

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract35Cl nuclear quadrupole resonance (NQR) was studied in 2,4‐dichlorobenzyl alcohol (2,4‐DCBA) and 2,6‐dichlorobenzyl alcohol (2,6‐DCBA). The NQR spectrum of 2,4‐DCBA show four lines and that of 2,6‐DCBA two lines. The temperature dependence of the NQR frequencies from 77 K up to the respective melting points was studied. An order–disorder transition was observed in 2,6‐DCBA around 215 K. Torsional frequencies and their temperature coefficients were calculated using the temperature dependence of the NQR frequencies, and were compared with the laser Raman spectra obtained at r

ISSN:0749-1581    

DOI:10.1002/mrc.1260300707

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of analogues of the antihistaminie agent phenindamine and its precursors are interpreted in terms of structure and geometry. Points of interest are the conformations of 4‐piperidinol and dihydro‐1‐pyrindene(diene) intermediates, and the configuration of the hexahydro analogue of phenindamine and its corresponding product of equilibration. Results of an antihistamine evaluation test are pres

ISSN:0749-1581    

DOI:10.1002/mrc.1260300708

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractAn ESR spectrum is observed when a sample of polyacrylonitrile powder is dissolved in a dimethyl sulphoxide solution of nitrosobenzene at room temperature. However, the spectrum is not associated with the trapping of occluded radicals from within the polymer latex, but with the hydrogen atom adduct. [Similarly, when an aqueous emulsion of poly(methyl methacrylate) is added in place of the polyacrylonitrile powder the spectrum of the hydrogen atom adduct is again observed.] Experiments in dimethyl‐d6sulphoxide indicate that the hydrogen atom does not originate from the solvent. At higher temperatures (383 K) the spectrum of a mixture of the hydrogen atom and methyl radical adducts is observed. Experiments in dimethyl‐d6sulphoxide show that the latter radical originates from the solv

ISSN:0749-1581    

DOI:10.1002/mrc.1260300709

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractHomo‐ and heteronuclear 2D NMR techniques were used to elucidate the structure of a novel pentaester of 19‐hydroxyingol fromEuphorbia marginataseeds. The diterpene skeleton was identified by1H 1D and 2D COSY spectra. Heteronuclear 2D13C1H shift correlation spectroscopy was used to assign the13C signals. The position of the esterified hydroxymethyl group at C‐10 was identified by NOE difference spectroscopy. The nature of the five ester groups and their corresponding positions on the diterpene skeleton were identified by a combination of long‐range 2D13C1H correlation experiments and13C spectra with1H selective

ISSN:0749-1581    

DOI:10.1002/mrc.1260300710

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe13C NMR data for tricyclic and bicyclic diaziridines with condensed five‐ and six‐membered rings are interpreted and compared with the forecast of the C13‐NMR/IR data‐base (successor: SPECINFO data‐base). There are large differences in chemical shifts and large deviations in the forecasts. Bond angles from semi‐empirical AM1 calculations with geometry optimization correlate with the observed shifts. Similar behaviour is found for some known bicyclic diaziridines, and this is also discussed together with some known13C shift variations in other diaziridines and bicyclic hydrocarbons. It is suggested that the widely used data‐base should include subset search facilities in order to minimize the risk of misassignments. This would allow specific effects, such as those of bond angles in cyclic compounds, to be taken into

ISSN:0749-1581    

DOI:10.1002/mrc.1260300711

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY