摘要:

AbstractThe1H NMR 270‐MHz spectra of substituted 2‐phenylthiazolidines were recorded and the substituent‐induced chemical shifts (SCS) of the benzylic proton plotted against σ, the correlation coefficient being 0.801 and −ρ = 10.29 Hz. Halogens show deviations in the SCS plots. When the halogen‐substituted derivatives are omitted, the correlation with σ is greatly improved. The applicability of dual‐substituent correlations using Swin‐Lupton parameters (FandR) and Taft's σ1, σRparameter

ISSN:0749-1581    

DOI:10.1002/mrc.1260280902

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

Abstract71Ga and27Al NMR and clay mineral pillaring studies were used to investigate the hydrolysis of Al(H2O) 63+–Ga(H2O) 63+solutions, mixed in an Al:Ga mole ratio of 12:1, and confirmed the formation of the previously proposed GaO4Al12(OH)24(H2O) 127+polyoxycation. This species has been found to be formed in marked preference to both AlO4Al12(OH)24(H2O) 127+and the previously identified GaO4Ga12(OH)24(H2O) 127+ions, and further to have a much higher thermal stability in solution than either of these. It is suggested that the reason for the increased stability of the ‘GaAl12’ species is that the substitution of a larger metal into the central tetrahedral position has resulted in the formation of a less dist

ISSN:0749-1581    

DOI:10.1002/mrc.1260280903

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe17O NMR spectra of six different arylmethylenemalonaldehydes were measured for various solvents and temperatures. The17O NMR chemical shifts and line widths of the carbonyl oxygens of the malonaldehyde fragment show a clear variation in the series of monoaryl compounds studied. The differences between the17O NMR chemical shifts of the formyl oxygens correlate well with two conformationally dependent1H–1H and1H–13C coupling constants for the same compounds. Molecular mechanical calculations were also performed in order to relate the present data with the conformational preferences of the malonaldehyde fragment of the arylmethylenemalonaldehy

ISSN:0749-1581    

DOI:10.1002/mrc.1260280904

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe application of a non‐refocusing INEPT pulse sequence in119Sn NMR spectroscopy allows the determination ofnJ(119Sn,1H) values by comparison of the observed patterns with calculated spectra. It gives an easy access tonJ(119Sn,1H) values in butyltin derivative

ISSN:0749-1581    

DOI:10.1002/mrc.1260280905

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractIt is demonstrated that the Müller and Bolton type of multiple‐quantum heteronuclear shift correlation is a promising tool for stereosequence assignments of polymers. Slight modification of the basic MQ pulse sequence results in a 2–3‐fold gain in sensitivity compared with the conventional single‐quantum spectra while retaining the one‐quantum frequency scale in theF

ISSN:0749-1581    

DOI:10.1002/mrc.1260280906

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of D‐amygdalin, a cyanogenetic disaccharide accumulated in food plants, were assigned using a combination of NMR techniques. Methods applied include standard1H–1H COSY, proton zero quantum coherence (ZQCOSY), 1D NOE, broad‐band decoupled1H–13C chemical shift correlation and long‐range1H–13C chemical shift correlation. ZQCOSY was especially useful in assigning the closely spaced sugar resonances, and long‐range1H‐13C chemical shift correlation allowed sequencing of the monosaccharide rings. Coupling constants useful in conformational analysis are derived from highly digitized1H 1D spectra and 2DJ‐resolved spectroscopy. The1H and13C chemical shifts and coupling constants indicate that the β‐D‐glucopyranose rings of D‐amygdalin adop

ISSN:0749-1581    

DOI:10.1002/mrc.1260280907

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractOrientation of proton spin systems relative to one another in polynuclear aromatics through the use of1H homo‐nuclear nuclear Overhauser effects (NOE) detected by heteronuclear multiple quantum correlation (HMQC‐NOESY) at natural abundance is reported. The experiment was explored as a potential alternative for problems in which a solution cannot be obtained by more conventional methods. Optimization of the HMQC‐NOESY experiment is disc

ISSN:0749-1581    

DOI:10.1002/mrc.1260280908

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe motional behaviour of 5‐nitro‐2‐(2‐pyridinylthio)pyridine (NPTP) was ananlysed by13C NMR spin‐lattice relaxation times (T1). The analysis of the experimentalT1data was performed by using an analytical model to describe the overall and internal motions fo the molecule. The results showed that on exchange exists between the two ‘enantiomeric’ preferred conformations of the molecule, which therefore assumes an enhanced conformationally rigid character in the liquid phase. The motional parameters, derived by the fitting procedure of the relaxation times, showed that strong intermolecular interactions occur in the liquid phase for NPTP and that, in particular, the dipole moment of the mitropyridine ring contributes greatly in determinating the motional dyn

ISSN:0749-1581    

DOI:10.1002/mrc.1260280909

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe full assignment of the ambient‐temperature high‐field1H NMR spectrum for the reduced form of a repeat‐unit β‐linked tetrasaccharide derived by keratanase digestion from keratan sulphate, GlcNAc(6‐SO4)13Gal(6‐SO4)14GlcNAc(6‐SO4)13Gal‐ol, was achieved using two‐dimensional COSY and RELAYED‐COSY experiments. The problem of the choice of the measurement temperature for1H NMR spectra from keratan sulphate oligomers and polymers is discussed. A modified protocol for the preparation of keratanase‐derived

ISSN:0749-1581    

DOI:10.1002/mrc.1260280910

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractCOSY and NOESY frequently fail when key proton signals are poorly resolved because of the proximity of the correlating off‐diagonal responses to the diagonal. Proton‐coupled heteronuclear multiple quantum relayed coherence spectroscopy (HMQC–TOCSY) and heteronuclear multiple quantum proton nuclear Overhauser effect (HMQC–NOESY) experiments to circumvent these problems are described. NMR data for a model carbocyclic nucleoside analog are presented for which assignments of resonances and stereochemistry were impossible by ‘conventional’ 2D NMR methods. Resonance and unequivocal stereochemical assignments were made, however, using the HMQC–TOCSY and HMQC–NOESY experiment

ISSN:0749-1581    

DOI:10.1002/mrc.1260280911

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY