摘要:

AbstractBoth selective (T1S) and biselective relaxation times (T1BS) were measured for the sulphur containing alkaloids, guinesine‐A, ‐B and ‐C (Ia, Ib and Ic). Their configurations and conformations were determined using the interproton distances (rij) derived from the cross‐relaxation times (σij), which were obtained from the observedT1SandT1BSvalues. Their configurations are concluded to be 3′,4′‐cis‐2,3′‐erythro(Ia), 3′,4′‐cis‐2,3′‐threo(Ib) and 3′,4′‐trans‐2,3′‐erythro(Ic), which are consistent with the results from x‐ray analyses and1H NOE experiments. The preferred conformations in CDCl3

ISSN:0749-1581    

DOI:10.1002/mrc.1260290802

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe use of 2‐fluoro‐2‐phenylacetic acid as a chiral derivatizing agent allowed the distinction, by means of fluorine NMR spectroscopy, of enantiomers of alcohols L1CH(OH)L2converted into the diastereoisomeric esters PhCHFCO2CHL1L2. The δF(RR) and δF(RS) fluorine chemical shifts of diastereoisomeric esters obtained from series of alcohols containing a substituted‐phenyl group (L1or L2= ZPh), and the ΔδF chemical shift differences, were linearly related to the Hammet σ parameter of Z. The ΔδF originates from the different electronic effects of L1and L2groups on the fluorine atom, through space, in a minor conformation. A classification of the ZPh effects on δF with respect to Ph is obtained. The configuration of substituted‐phenyl secondary alcohols, ZPhCH(OH)L, can be determined with the aid of the δF values of esters formed with PhCHFCO2H if the configuration of the unsubstituted alcohol

ISSN:0749-1581    

DOI:10.1002/mrc.1260290803

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractEstablished NMR criteria from1H,13C and 2DJ‐resolved13C NMR spectra, and also1H{1H} NOE experiments, were used to determine the constitution and configuration in a series of substituted penta‐1,3‐dien

ISSN:0749-1581    

DOI:10.1002/mrc.1260290804

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe1H (300 MHz) and13C (75.5 MHz) NMR spectra (CDCl3) ofN‐desmethyl‐N,O‐diacetyl‐α‐metazocine showed two (E,Z)‐amide diastereomers (ratio ≈︁ 1 : 2, respectively). All four vicinal proton‐proton coupling constants in each NCH2CH2C moiety were readily measured owing to effective chemical shift dispersion caused by the acetamido function. All vicinal coupling constants were also measured in the E. COSY 2D NMR spectrum. Comparison of the vicinal coupling constants involving sp2‐N piperidine ring protons in the (E,Z)‐amides and the corresponding values involving sp3‐N piperidine ring protons in morphine free base and hydrochlorideN‐methyl diastereomers shows them to be similar. TheR‐factor method was used to estimate a 54(1)° value for theNCH2CH2Cdihedral angle in the sp2‐N piperidine ring for both solution‐stateE,Z‐diasteromers. The corresponding dihedral angle within the sp3‐N piperidine ring in solid‐state (±)‐6‐desmethyl‐8‐deoxy‐α‐metazocine · HCl was found to be 53.8° by x‐ray crystallography. Both sp2and sp3N‐hybridrization seem to afford basically the same sl

ISSN:0749-1581    

DOI:10.1002/mrc.1260290805

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of triangulanes, the unique class of hydrocarbons constructed from spiroannulated cyclopropanes, were analysed, and correlations were revealed between their structures and13C chemical shifts. The procedure for the configurational assignment in triangulanes based on the13C NMR spectral data is described.

ISSN:0749-1581    

DOI:10.1002/mrc.1260290806

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractFour dicyclohexyl compounds were studied, one of which is a traction fluid and the remainder have related structures in which the cyclohexane rings are separated by two or three carbon atoms. Carbon‐13 NMRT1and NOE data were obtained for the four compounds at 22.50 and 100.62 MHz over a wide temperature range. The data were fitted simultaneously to either a reduced Lorentzian spectral density or to a ‘model‐free’ two‐correlation time spectral density. For the first time it has been possible to observe the tracking from the full ‘model‐free’ two‐correlation time spectral density to the reduced Lorentzian spectral density. From the correlation times and activation energies derived from these fittings, it can be concluded that all the compounds have semi‐rigid structures. Computer modelling of the structures and molecular mechanics calculations of the rotational barriers gave results in agreement with those from the NMR data. Similarly, it was found that the friction coefficients of the compounds correlate with the NMR and molecular mechanics conclusions, namely that the increased rigidity produced by the introduction of methyl groups into the linkage between the cyclohexane rings leads to a more effective traction fluids. Hence it seems to be feasible to design new traction fluid

ISSN:0749-1581    

DOI:10.1002/mrc.1260290807

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe primary structure of the de‐O‐acetylated glucuronoxylomannan isolated fromCryptococcus neoformansserotype D was characterizedde novoby NMR spectroscopy. Assignment of the1H and13C spectra of the polysaccharide involved a combination of 2D NMR experiments including double‐quantum‐filtered {1H,1H} COSY, {1H,1H} TOCSY and1H‐detected {1H,13C} heteronuclear multiple quantum coherence spectroscopy. The sequence of the glycosyl residues, including the linkage positions, was deduced by {1H,1H} rotating‐frame NOE (ROESY) spectroscopy. The serotype‐D glucuronoxylomannan was found to be a branched polymer with a repeating pentasaccharide unit of the followi

ISSN:0749-1581    

DOI:10.1002/mrc.1260290808

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractN‐Acetylation of solasodine gives only one rotamericN‐acetyl derivative compared withN‐acetyl‐3‐methylpiperidine, which exists in solution as two equally populated rotamers. The1H and13C NMR spectra (CDCl3) ofO,N‐diacetyl‐ andO‐acetyl‐N‐benzoylsolasodine indicate significant deviations from F‐ring chair geometry. Opening of the F ring of these derivatives in CDCl3solution at 25°C, to give the corresponding furosta‐5,20(22)‐diene derivatives, was ascer

ISSN:0749-1581    

DOI:10.1002/mrc.1260290809

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe application of the3J(HCXC) couplings in 3‐arylideneflavanones and 3‐arylidenethioflavanones allows a semi‐quantitative estimation of the conformationa

ISSN:0749-1581    

DOI:10.1002/mrc.1260290810

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe equilibrium mixture of thecisandtransisomers of caprylolactam (1‐azacyclononan‐2‐one), was studied by1H and13C NMR spectroscopy at various temperatures. The exchange between corresponding carbons in the two isomers in solution was studied by 2D NOE. Assignments were made for all13C lines of thecisandtransisomers in CDCl3, CD3OD and C5D5N by 2D NMR. The conformations and conformational processes were studied by low‐temperature NMR. Thetransisomer was shown to exist in at least two different conformations in solution. In addition to the high barrier interconversion between thecisandtransisomers, two different conformational processes were found for thetransisomer in the temperature range −140 to +60°C and one for thecisisomer. The conformational processes in solution are identified as (1) geminal1H exchange in thecisand thetransisomers: for thecisisomer with a coalescence temperature ofca.−70°C a free energy of activation of 40 kJ mol−1and for thetransisomer with a coalescence temperature ofca.+40°C a free energy of activation of 61 kJ mol−1; and (2) a low‐temperature process interconverting twotransconformations with a coalescence temperature ofca.−120°C and a free energy of activation of 29 kJ mol−1, observed in both

ISSN:0749-1581    

DOI:10.1002/mrc.1260290811

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY