摘要:

Abstract35Cl NQR (77 K) spectra for two groups of compounds, C6H5COCH3‐nClnandp‐ClC6H4COCH3‐nCln, are reported. The frequencies were assigned to individual chlorine atoms in the molecules. Polar effects and mechanisms of conjugation in the molecules are discussed. The influence of the polar carbonyl group on the electronic structure of the molecule and the NQR frequency was studied in d

ISSN:0749-1581    

DOI:10.1002/mrc.1260250702

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

Abstract17O NMR chemical shifts of 2‐oxo‐1,3,2‐dioxathiane and 13 of its methyl‐substituted derivatives are reported. The chemical shifts depend strongly on temperature and to a much smaller extent on concentration. As a whole, however, they strongly support the predominance of chair conformations in these compounds and indicate some misinterpretations in a previous

ISSN:0749-1581    

DOI:10.1002/mrc.1260250703

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractA35Cl NQR study of 2‐chloro‐3‐pyridinol showed the presence of four NQR signals at 77 K. One of the lines showed a positive temperature coefficient of the NQR frequency.1H NMR studies showed the presence of intramolecular hydrogen bonding, and the anomalous NQR temperature dependence has been explained in terms of Bayer and hydrogen bond effects. The room temperature x‐ray structure and the low‐temperature NQR data suggest the presence of a phase t

ISSN:0749-1581    

DOI:10.1002/mrc.1260250704

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe protonation of acetone in water for a wide range of compositions of the binary mixture was studied by multinuclear NMR spectroscopy. Formation constants (K1andK2) and13C,17O and1H chemical shifts of the 1:1 and 1:2 complexes were evaluated. The correlation of the1H chemical shift of uncombined water with its concentration, Δ=A+BIn [H2O]eq, recently derived for the trimethyl phosphate‐water system, was verified. A measure of the fraction of monomer species existing in the uncombined water at each composition was obtained. The results are discussed with respect to the structure of wat

ISSN:0749-1581    

DOI:10.1002/mrc.1260250705

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractFour different pulse sequences for proton‐carbon shift correlation via1J(CH) couplings are compared using amacrolide as a practical example. These are the COLOC sequence, a new improved variant of COLOC, the 2D‐DEPT‐COSY sequence and its new constant‐time variant. It emerged that the 2D‐DEPT‐COSY and the modified COLOC sequences are the most appropriate for the purpose of routine proton‐carbon shift correlation via di

ISSN:0749-1581    

DOI:10.1002/mrc.1260250706

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractNorbornane‐ or norbornene‐fused 2‐aryldihydro‐1,3‐oxazines, ‐1,3‐oxazin‐2‐ones and – 1,3‐oxazine‐2‐thiones were synthesized and studied by1H and13C NMR spectroscopy to reveal the spectral effects of the saturation of the skeleton,diexoordiendoring annellation and isomerism in compounds containing the oxygen and nitrogen hetero at

ISSN:0749-1581    

DOI:10.1002/mrc.1260250707

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of equilibrium mixtures formed between sulphur dioxide andN‐methylbenzenamine,N,N‐dimethylbenzenamine andN,N‐diethylbenzenamine were obtained. The analysis of the spectral data indicates that the interaction of the amines with the Lewis acid occurs by means of the lone pair mainly localized on the nitrogen atom, and that the complexes can be considered as labile on the time scale of the exper

ISSN:0749-1581    

DOI:10.1002/mrc.1260250708

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

Abstract1H NMR studies at 250 MHzand13C NMR studies at 62.8 MHzon the synthetic nonapeptide fragment of type III collagen, Gly‐Lys‐Hyp‐Gly‐Glu‐Hyp‐Gly‐Pro‐Lys (CP9), have been carried out in aqueous solution and DMSO‐d6. The resonances are assigned with the help of 2D correlated spectroscopy, pH titrations by following the characteristic pKvalues exhibited by protons adjacent to ionization sites and one‐dimensional (1D) spin decoupling techniques. Chemical shifts of the proline and hydroxylproline carbon atoms indicate that thetransconfiguration about the three X—Pro and XHyp peptide bonds is strongly favoured in all cases, although the minorcisresonances accounting for about 10% of the Pro and Hyp intensity can also be observed. In addition, there appears to be no significant pH sensitivity of thecis⇌transequilibrium. Addition of aluminium causes changes in the spectra, indicating specific interactions with carboxylates of the glutamyl and lysyl residues, as well as a change for both hydroxylproline residues. These data are interpreted by the formation of a 1:2 stoichiometric complex (AlIII‐CP9). the implication of these results with respect to the effect of aluminium in the t

ISSN:0749-1581    

DOI:10.1002/mrc.1260250709

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe temperature dependence of paramagnetic shifts induced for proton resonances has been investigated for lanthanide (Dy, Ho and Yb) complexes of L‐carnosine. Two different methods of data reduction were used to separate contact, pseudo‐contact and diamagnetic contributions to the paramagnetic shift, one using induced bound shifts and the other based on temperature plots of the induced shift ratios. These studies revealed that diamagnetic effects, which include conformational changes, inductive effects and direct field effects, cannot be neglected. In the Dy, Ho and Yb complexes the side‐chain is folded, but isomorphous replacement and axial symmetry are ret

ISSN:0749-1581    

DOI:10.1002/mrc.1260250710

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractTheJ‐modulated spin‐echo pulse sequence can be used for the approximate estimation of one‐bond CH coupling constants in complicated spectral regions. The usefulness of this technique for spectral assignment purposes is demonstrated for a beta‐lactam

ISSN:0749-1581    

DOI:10.1002/mrc.1260250711

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY