摘要:

AbstractHigh‐resolution carbon‐13 NMR spectra were obtained for three solid fluorinated steroids. Assignments were carried out using several approaches, including two‐dimensional spectra of the compounds in solution. Solid‐state and solution‐state chemical shifts are compared. Signals from one of the fluorine‐containing carbons in each compound show the effect of interplay between shielding, dipolar and indirect scalar (J) coupling tensors. One sample is found to be a mixture of two polymo

ISSN:0749-1581    

DOI:10.1002/mrc.1260330702

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA chemical shift analysis of the13C NMR spectra of more than 50 acyclic sulphonic acids, alkali metal sulphonates and methyl esters was carried out. Chemical shift increment systems withn‐alkanes as reference molecules were established for linear alkanesulphonates and alk‐2‐enesulphonates. Some short‐chain fluorinated sulphonic acids were also studied, especially pentafluorothio derivatives. CF spin‐spin coupling constants were determined. Pauling electronegativity values for SO3H and SF5groups were derived from α chemical shif

ISSN:0749-1581    

DOI:10.1002/mrc.1260330703

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractLead tetraacetate one‐electron oxidation of nine differentN‐alkoxy‐2,6‐dinitroanilines substituted with trifluoromethyl, methyl and nitro groups in position 4 yielded aminyl radicals for which hyperfine couplings were measured by ENDOR and TRIPLE resonance spectroscopy. The optimum temperature range for proton ENDOR and general TRIPLE resonance measurements of aminyl radicals was 210–250 K and for nitrogen ENDOR 260 K in toluene. Further lowering for the temperature rapidly decreased the EPR intensity. The concentration of the sample and the amount of oxidant were optimized for obtaining ENDOR spectra. The relative signs of the hyperfine couplings of nitrogens, fluorines and protons were determined in the basis of general TRIPLE resonance experiments. The oxidation ofN‐methoxy‐N‐2,6‐dinitrophenylamine andN‐ethoxy‐N‐2,6‐dinitrophenylamine with lead tetraacetate produced first the aminyl radical of the respective 2,6‐dinitro compound at low temperature (below 260 K) and very soon afterwards the aminyl radical of the respective 2,4,6‐trinitro compound, by a route in which hydrogen has to be removed from the system. Rotational correlation times were estimated forN‐methoxy‐andN‐ethoxy‐N‐2,4,6‐trinitrophenylaminyl radicals. Nitroxyl radicals were detected only under condition

ISSN:0749-1581    

DOI:10.1002/mrc.1260330704

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe substituent effect on the proton hyperfine splitting constants (hfsc) of the charge‐transfer complexes of Grignard reagents (RMgBr, R = CH3, C2H5, CH3CHCH) with seven 3‐substituted 9,10‐phenanthroquinones is reported. A back‐donation bonding interaction between phenanthrenesemiquinonate anion radical π*and the magnesium p orbital is revealed by the hfs

ISSN:0749-1581    

DOI:10.1002/mrc.1260330705

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn order to perform the analysis of the components contained in fossil fuels, carbon assignments of new methylated derivatives of tetralin and indan were obtained. Their chemical shifts were calculated by applying additivity rules.

ISSN:0749-1581    

DOI:10.1002/mrc.1260330706

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractProton and carbon NMR data are provided for 21 ring A and ring B cyclosteroids and cyclopropano (or methylene) steroids. Shift assignments were made using standard 2D NMR techniques, while ring A proton subspectra were extracted with a 1D TOCSY experiment. Coupling constants were obtained from iterative spin system simulation of these sub‐spectra. Ring A conformations were determined from the two‐ and three‐bond proton‐proton couplings and NOE measurements. The utility and limitations of extended Karplus‐type equations, the effect of cyclopropyl groups on vicinal and geminal couplings and cyclopropane‐induced chemical shifts ar

ISSN:0749-1581    

DOI:10.1002/mrc.1260330707

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractMultiple‐field carbon‐13 relaxation data are reported for melezitose, a trisaccharide consisting of two α‐linked glucose residues attached at positions 2 and 3 to a β‐linked fructofuranose residue. Values forT1and NOE were measured at 4.7, 9.4, 11.8 and 14.1 T and transverse relaxation rates at 4.7 and 9.4 T. The measurements were carried out by means of standard techniques and by polarization transfer (INEPT) enhanced methods. The relaxation data were interpreted with the Lipari‐Szabo ‘model‐free’ approach. It was found that the relaxation data of the ring carbons can be described by the use of the truncated form of the Lipari‐Szabo equation. The global correlation time and order parameter for melizitose were calculated at two temperatures. For the exocyclic CH2carbons, fits to obtain a local correlation time are reported. For three out of the four exocyclic carbons, a fast correlation time is obtained and their order parameter is lower than that for the ring carbons. The fructose C‐1 exocyclic carbon does not seem to display the same local motions as the other CH2groups, and a higher order parameter is obtained indicating hindered local mo

ISSN:0749-1581    

DOI:10.1002/mrc.1260330708

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractTheaflavin, theaflavin monogallate and theaflavin digallate were isolated from black tea leaves and studied by 1D and 2D NMR techniques, thus allowing unambiguous assignment of the1H and13C resonances of these complexes. Earlier studies have not yielded13C data of equal reliability, especially for the benzotropolone moiety of these molecules, and consequently the data given here will be of use in future studies of natural products isolated from tea. The utility of the 2D proton detected long‐range13C1H correlation experiment (HMBC) in the study of polyphenolic complexes is demonstrated by these resu

ISSN:0749-1581    

DOI:10.1002/mrc.1260330709

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe ABX spin systems of the [mono‐13C]isotopomers with vinylic and phenylipso‐13C atoms of a number of symmetrical 1,4‐dihydro‐1,4‐diphenyl‐1λ5,4λ5‐diphosphinines were analysed. The substituent dependence of the absolute signs and magnitudes of2J(PC) between the two31P nuclei and two vinylic13C atoms and of the4J(PC) and3J(PP) are reported.13C isotope effects on δ(31P) and3J(P

ISSN:0749-1581    

DOI:10.1002/mrc.1260330710

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe nuclear spin relaxation rate of the quadrupolar14N nuclei inN,N′,N″‐tris(trimethylsilyl)borazine (1) is surprisingly slow [T1(14N)=0.1 s]. This allows one to measure1J(29Si14N) (9.6 Hz) directly from the29Si NMR spectra and also to compare signs of coupling constants1J(29Si14N) (0) by 2D29Si/1H HETCOR experiments. Since the transverse relaxation timeT2(14N) in 1 is governed by scalar relaxation of the second kind, the magnitude of1J(14N11B) can be evaluated (23 ± 0.5 Hz).11B,14N and29Si NMR data forN,N′‐bis(trimethylsilyl)borazine (2) were also obtained, and11B and14N NMR spectra of the parent borazine [HBNH]3(3), and of [HBNMe]3(4) were remeasured. Calculation of the tensor components of the14N electric field gradient shows thateqzzin 1 and in 2 for14N(Si) is significantly smaller than for other borazines [HBNR]3, e.g. with R=H (3) or Me (4), in agreement with the experiment

ISSN:0749-1581    

DOI:10.1002/mrc.1260330711

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY