摘要:

AbstractThe13C spin‐lattice relaxation times and nuclear Overhauser enhancement factors of all‐trans‐retinal were measured in acetone‐d6at two different magnetic field strengths. The extent to which the chemical shift anisotropy mechanism was found to contribute to the relaxation rate of the quaternary olefinic carbons was between 23 and 37% at 4.70 T and between 48 and 66% at 8.45 T. Assuming anisotropic molecular motion and an asymmetric chemical shift tensor, the shielding anisotropies of carbons C‐5, C‐6, C‐9 and C‐13 were calculated to be 185, 172, 188 and 228 ppm, respectively. These are qualitatively similar to those obtained in a recent13C NMR study of all‐trans‐retinal in the solid state. In contrast, the quaternary aliphatic carbon C‐1 was much less relaxed by the chemical shift anisotropy mechanism (contribution<11%). The relaxation of the proton‐bearing carbons was independent of the magnetic field and determined only by the dipole—dip

ISSN:0749-1581    

DOI:10.1002/mrc.1260250902

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractA modified long‐range heteronuclear chemical shift correlation pulse sequence which eliminates modulations of response intensity due to one‐bond proton‐carbon [1J(CH)] spin couplings is described. The ‘decoupling’ of one‐bond modulation has been accomplished through the use of a bilinear rotational decoupling (BIRD) pulse of the type 90°x(1H)‐τ‐180°x(1H)/180°x(13C)‐τ‐90°‐x(1H) midway through the second magnetization transfer delay, Δ2.One‐bond modulation of response intensities over a range of optimization values is demonstrated for the simple alkaloid norharmane when long‐range optimization of the conventional heteronuclear chemical shift correlation pulse sequence is employed. The modified pulse sequence described eliminates one‐bond modulations over the same range of optimization values. Slower modulations which arise due to long‐range couplings other than that optimized for are present in both experiments.Removal of the effects of one‐bond modulation represents a potentially significant improvement in the utility of long‐range heteronuclear chemical shift correlation experiments as a tool in spectr

ISSN:0749-1581    

DOI:10.1002/mrc.1260250903

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe structures of open‐chain bis‐Reissert analogues and their salts were investigated using13C NMR spectroscopy. Evidence is presented to show that the former exists in the acyclic form in solution. Detailed structural studies and the13C NMR data clearly show that, in solution, the open‐chain bis‐Reissert salt analogues exist predominantly as the amino t

ISSN:0749-1581    

DOI:10.1002/mrc.1260250904

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

Abstract13C,1H and31P NMR investigations were carried out to confirm the stereochemistry of novel bis[(4R,6R)‐4,6‐dimethyl‐1,3,2‐dioxaphosphorinan‐2‐yloxy]alkanes. The13C NMR spectra exhibited second‐order features at room temperature. Substantial coupling was found between P atoms six bonds apart. The possibility of a through‐space contribution was tested. Spatially close P atoms and the strongly electronegative P substituents (oxygen atoms) are thought to be responsible for the enhance

ISSN:0749-1581    

DOI:10.1002/mrc.1260250905

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractTherαstructures of ethylene and 1,1‐difluoroethylene have been determined by NMR of partially oriented molecules, considering the interaction between the solute molecule and the liquid crystal solvent which leads to a correlation between molecular vibration and rotation. The analysis of the data also provides the interaction parameters which characterize the torques acting on the individual molecular bonds, deforming and simultaneously orienting the solute. A linear relationship between the interaction parameters for the C  H bonds of the two solutes and methane in the same solvents has been f

ISSN:0749-1581    

DOI:10.1002/mrc.1260250906

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe13C chemical shifts for 2,7‐, 1,8‐ and 1,6‐diazabiphenylenes are reported, together with some coupling constants and the13C chemical shifts of a benzothiophene analogue of biphenylene. The results can be explained by the existence of a paramagnetic ring current in the four‐membered ring of the nitrogen‐containing compounds which is absent in the case of the benzothiophene. A possible explanation i

ISSN:0749-1581    

DOI:10.1002/mrc.1260250907

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractProton and13C NMR parameters have been determined for phenyldibenzophosphole and its oxide, sulfide, selenide and W(CO)5complex from high‐resolution one‐ and two‐dimensional (COSY, HETCOR and 2DJ) experiments at 4.7, 7.1 and 9.4 tesla. Assignments of chemical shifts and coupling constants have been made and verified by computer simulation of the proton spectra. The data are discussed in relation to the geometry and electron density at phosphorus and the diamagnetic anisotropy of the W(CO)5

ISSN:0749-1581    

DOI:10.1002/mrc.1260250908

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe 500 MHz1H spectra of the 3‐methyl ethers of estrone, estradiol and their 14α‐methyl analogues were assigned by proton decoupling and analysed by second‐order calculations for chemical shifts and coupling constants. Introduction of a 14α‐Me group effects consistent deshielding of 1,3 diaxially disposed protons. Coupling constant values show characteristic changes for ring D protons, and suggest that some minor perturbation in the H‐9α, ‐11α, ‐11β region is caused by the addit

ISSN:0749-1581    

DOI:10.1002/mrc.1260250909

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractTwo O‐linked glycopeptides were isolated by protease digestion of calf fetuin. Using13C and1H NMR spectroscopy, it was established that both carry identical trisaccharide side‐chains, but they were found to possess different peptide moieties. Therefore, they must originate from different regions of the polypeptide backbone of fetuin. The two glycopeptides carry a total of three oligosaccharide chains, in accordance with previously published data. One glycopeptide was found to carry two side‐chains: one is linked to a serine and the other to a threonine that are separated by one alanine only. The other glycopeptide carries one sugar chain linked to a serine residue. It was not possible to isolate any glycopeptide which contained a second sialic acid residue directly linked to theN‐acetylgalactosamine, as reported earlier. Some long‐range chemical shift effects were observed in the NMR spectra of the glycopeptide, indicating a specific conformation for this glycopeptide as a result of the proximity of the two oligosaccharide si

ISSN:0749-1581    

DOI:10.1002/mrc.1260250910

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe geometry of pyrrolidine and 3 hydroxypyrrolidine CoTPP complexes has been investigated by1H NMR spectroscopy. The observed couplings and ring current shifts for pyrrolidine‐CoTPP are consistent with an envelope conformation with the nitrogen atom out of the ring plane and equatorial coordination of the cobalt atom. A complete analysis of the spectrum was not possible owing to close‐coupling of the β‐protons.For 3‐hydroxypyrrolidine CoTPP two components in the ratio 85 : 15 were observed in the proton spectrum. The spectra of both compounds were completely analysed to give all the couplings in the five‐membered rings, and from these the ring conformations were deduced. The major (endo) component exists in an envelope conformation with C‐2 out of the plane of the other atoms, and the hydroxy groupcisto the NH proton, both in pseudo‐axial orientations. The minor (exo) component is also in an envelope conformation, with C‐5 out of the plane of the other atoms and the hydroxyl group nowtransto the NH proton.The energy difference ofca1 kcal mol−1(4 kJ mol−1) in favour of theendocomponent was reproduced by theoretical (MNDO) calculations for protonated hydroxypyrrolidine, but not for the free base. This suggests that the stabilization of theendocomponent is due to the electrostatic attraction of the hydroxy group and positively c

ISSN:0749-1581    

DOI:10.1002/mrc.1260250911

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY