摘要:

AbstractHigh‐field1H NMR studies of himachalol (1) have been carried out by two‐dimensional NMR methods. The stereochemical aspects of this molecule were studied through the application of stereospecific coupling constants, the nuclear Overhauser effect and lanthanide‐induced chemical shifts. Complete and unambiguous13C chemical shift assignments of 1 have been made for the first time by using two‐dimensional heteronuclear (1H13C) correlation NMR spectroscopy, DEPT, broad‐band proton decoupling and selective heteronuclear spin decoupling13C NMR methods. Complete13C chemical shift assignments of isocentdarol, centdarol and centdarone have also been made using some of the above techniques and their stereostructures have bee

ISSN:0749-1581    

DOI:10.1002/mrc.1260260112

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

Abstract13C NMR chemical shifts for some α‐heterosubstituted acetones were recorded. The carbonyl carbon shieldings are discussed in the light of the substituent electronic effects and were also empirically estimated by Tanakaet al.'sequation. An approximate linear relationship was observed between the13C and17O chemical shifts. A nonadditivity of substituent chemical shifts was observed for the α‐methylene carbon, and attributed to intramolecular interactions between the α‐heteroatom and the carbon

ISSN:0749-1581    

DOI:10.1002/mrc.1260260113

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe 400 MHz1H NMR spectra of fourcisisomers of synthetic renierapurpurin‐20‐al (χ,χ‐caroten‐20‐al) were completely assigned by application of two‐dimensional proton‐proton chemical shift correlated spectroscopy (2D COSY) with high digital resolution ofca0.4 Hz per point by acquisition of only the olefinic part of the spectra. Connectivities to the methyl and aldehyde protons absorbing outside the measured range were also obtained owing to the folding of their cross‐peaks along theF1axis. Nuclear Overhauser difference experiments and consideration of chemical shift changes were applied to derive unequivocally the 13‐cis(13E), 7,13‐di‐cis(7Z), 13,7′‐di‐cis(7′Z) and 13,9′‐di‐cis(9′Z) configuration of the isomers. The1H‐detected one‐bond1J(CH) and long‐range2,3J(CH) multiple quantum coherence heterocorrelated 2D spectra of 1.2 mg of the main 13‐cisisomer were acquired and the13C signals partly assigned. The structural consequences with respect to othe

ISSN:0749-1581    

DOI:10.1002/mrc.1260260114

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractA variety of isotopically labelled and/or substituted flavins have been converted into their corresponding radical states. Cation and neutral radicals were generated chemically and anion radicals were obtained electrochemically. By performing ENDOR and TRIPLE resonance experiments, complete sets of hyperfine coupling constants including their signs were accessible. The hyperfine data allowed (a) identification of the radical state present, (b) information to be obtained about the preferred conformational arrangements of the substituents and (c) conclusions to be drawn about the influences of the substituents on the spin density distributions of the different radical states.

ISSN:0749-1581    

DOI:10.1002/mrc.1260260115

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractCarbon‐13 NMR chemical shifts of a series of α‐monosubstitutedN,N‐diethylacetamides [YCH2C(O)NEt2, Y = Me, Cl, Br, I, OMe, SMe, and NMe2] are reported. The α‐methylene and carbonyl carbon chemical shifts are correlated with the Pauling electronegativities (Ep) and Charton's localized electrical parameters (σL), respectively. The non‐equivalence of the chemical shifts for thesynandanti‐N‐alkyl carbon atoms are attributed to the electric field and steric compression effects and also to the YCH2cisan

ISSN:0749-1581    

DOI:10.1002/mrc.1260260116

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractTwo methods are examined which allow a NOESY experiment to be performed involving only a specific site of the molecule labelled by a heteronucleus. They involve the merging of a classical phase‐sensitive NOESY experiment with either an INEPT sequence, which transfers1H magnetization to a coupled heteronucles, or a multiple quantum filtering sequence which allows the selection of only the1H resonances which are coupled to the heteronucles. The two methods are first compared on two small molecules, non‐labelled alanine and [U‐13C]alanine, particularly with respect to the signal‐to‐noise ratio. An example of the application of these methods on a 25000 molecular weight protein system (elastase‐peptide complex) is also given. The limitations of the methods, in particular in terms ofT2, ar

ISSN:0749-1581    

DOI:10.1002/mrc.1260260117

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

Abstractγgaucheeffects of 12‐substituted‐14β‐hydroxy‐ and 14α‐steroids were studied by1H and13C NMR spectroscopy. A linear correlation was found between the1H chemical shift of4H‐17 and the13C shift of C‐17 for C‐12‐substituted steroids. This correlation can be explained by

ISSN:0749-1581    

DOI:10.1002/mrc.1260260118

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of a series of novel 2(5H)‐furanones were studied. The assignments of the carbon resonances were made on the basis of chemical shifts, long‐range carbon‐hydrogen couplings, intarnal comparison and known reference so

ISSN:0749-1581    

DOI:10.1002/mrc.1260260119

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

ISSN:0749-1581    

DOI:10.1002/mrc.1260260122

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY

ISSN:0749-1581    

DOI:10.1002/mrc.1260260101

出版商:John Wiley&Sons, Ltd.    

年代:1988

数据来源: WILEY