ISSN:0749-1581    

DOI:10.1002/mrc.1260330102

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA combination of NMR experiments, including13C and15N DEPT, COSY, NOESY, HMQC and HMBC experiments, was used to assign the structures and stereochemistries of two isomeric bicyclo[2.2.2]octenedione derivatives produced by the reaction of perezone with thiourea, followed by treatment with silica gel. A possible mechanism of the reaction is suggested.

ISSN:0749-1581    

DOI:10.1002/mrc.1260330103

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe principal elements δiiof31P and77Se chemical shift tensors for the structural analogues bis(dineopentoxythiophosphoryl) diselenide (1) and bis(dineopentoxythiophosphoryl) disulphide (2) were calculated from spinning sideband intensities employing the MASNMR program. From analysis of the31P NMR data it was concluded that replacement of sulphur by selenium has little influence on shielding parameters, anisotropy Δδ and span Ω. The asymmetry η and skewkare very similar if the geometry of SPXXPS unit (X = S, Se) is not changed.77Se NMR data are discussed in terms of PSeSeP unit geometry. The static spectra were recorded employing the CPECHO pulse sequence. It was found that this technique is useful both for the lineshape analysis and the calculation of the second moment. The experimental values ofM2dare 0.387 kHz2for diselenide 1 and 0.495 kHz2for disulphide 2. These values are consistent with those calculated from the van Vleck equation for polycrystalline m

ISSN:0749-1581    

DOI:10.1002/mrc.1260330104

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe oxidation of 4‐methylcatechol by dioxygen and the subsequent reactions of the two nucleophiles OH−and MeO−with the oxidation products were studied by electron spin resonance (ESR) spectroscopy. These reactions are models for those of skin proteins with substituted 1,2‐dihydroxybenzenes (catechols) which produce the severe allergic contact dermatitis associated with plants such as poison ivy, poison oakd and the Japanese lac tree. The rates of formation of the primary and secondary semiquinone radical anions show a large kinetic deuterium isotope effect (ca10) at 20°C, which is ascribed to a slow deprotonation of the hydrogen bridged 4‐methylcatechol monoanion. There is a marked difference in regioselectivity for OH−and MeO−substitution of the 4‐methylcatechol monoanione; OH−reacts exclusively at the 3‐position whereas MeO−attacks at the 5‐position. This dissimilarity between two normally similar nucleophiles is also ascribed to the occurrence of hydrogen bridging between the substituting OH−at the 3‐position and the adjacent quinone oxygen at the 2‐position. The expected attack at the more electropositive 5‐position occurs with MeO−because no such hydrogen bonding can occur. Disubstitution occurs for OH−but not for MeO−, probably reflecting the

ISSN:0749-1581    

DOI:10.1002/mrc.1260330105

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractOne‐ and two‐dimensional magnetization‐transfer19F NMR methods were applied in a quantitative study of the fluoride exchange for uranyl(2+)‐fluoride complexes in aqueous solution. The applicability of these techniques and the classical lineshape analysis is discussed, and the quality of the results (rate constants and relaxation rates) obtained by the three methods is c

ISSN:0749-1581    

DOI:10.1002/mrc.1260330106

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of a series of dialkyl α‐anilinobenzylphosphonates and dialkyl α‐anilino‐(2‐hydroxybenzyl)phosphonates were measured. The assignment of the spectra was performed using a combination of31P‐13C and13C‐1H coupling constants and substituent‐induced chemical shifts. Long‐range phosphorus‐carbon couplings up to five

ISSN:0749-1581    

DOI:10.1002/mrc.1260330107

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractOne‐ and two‐dimensional1H NMR studies of low‐spin iron(III) geoporphyrins derived from the deoxophylloery‐throetioporphyrin series (the oil shale source) resulted in an unambiguous assignment of all resonances. Deoxophylloerythroetioporphyrin (DPEP) and its 17‐desethyl homologue were isolated from dictyonema shale as vanadyl complexes. They were demetallated and subsequently converted into iron(III) porphyrins under mild conditions. The 17‐propionic methyl ester analogue, i.e. deoxophylloerythrin methyl ester, was synthesized for comparative studies. A spectroscopic probe to identify iron(III) isocyclic porphyrins was established. The five‐membered isocyclic ring induced considerable asymmetry in the spin density distribution at the 3eπbonding orbitals, placing the unpaired electron on the dxzorbital located along the N‐21—N–23 axis. The temperature dependence of the hyperfine shift is consistent with the thermal equilibrium between two non‐degenerated electronic states (dxz)2(dyz)1↔(dxz)1(dyz)2. The new structural factor generating the asymmetric spin density distribution in low‐spin iron(III) porphyrin complex was determined. The hyperfine shift pattern of high‐spin iron(III) isocyclic geoporphyrins provided useful probes for their detection in iron geoporphyrin mixtures by1H NMR prior to their separation. Valuable information is derived from the number of observed signals ofmeso‐protons and characteristic, extremely downfield resonances of isocyclic ring hydrogens. Both features may be useful for the spectral identification of iron(III) porphyrins of the DPEP series from geological mate

ISSN:0749-1581    

DOI:10.1002/mrc.1260330108

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe NMR spectra (35Cl,79Br,81Br,127I and17O) of the tetrahedral perhalate anions XO4−(X  Cl, Br and I) were compared for the first time in acetonitrile solution, a medium in which the resonances are relatively sharp and in which no oxygen exchange occurs. Relaxation studies of the quadrupolar nuclei in these solutions at 24°C are reported and show that excellent spectra may be obtained at 0.1 M concentration; thus the observation of separate resonances for Cl16O4−and Cl18O16O3−represents the first reported instance of a35Cl secondary isotopic shift [1Δ35Cl(18.16O) = ‐0.090 ppm]. Enrichment with17O of all three ions was carried out and the1J(127I,17O) coupling constant (489 Hz) has been observed for the first time. The chemical shifts and coupling constants are discussed, especially in connection with the anomalous properties of the perbromate ion. Halogen chemical shifts for BrO3F, IF7and IF6+AsF6−are reported for t

ISSN:0749-1581    

DOI:10.1002/mrc.1260330109

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

Abstract2D31P,15N heteronuclear shift correlation, based on a non‐refocused INEPT pulse sequence with15N detection, was applied to a15N NMR study of the azadiphosphiridines 1‐5 which are formed by [2 + 1] cycloaddition of iminophosphines, RPNR′. The pulse sequence used allowed consistent assignment of both the31P and15N NMR spectra in one experiment; by a slight modification, also the signs of numerous31P‐15N coupling constants across one or two bonds could be determined. Comparison of the data with those of the azatriphosphetidine 6 (obtained from ID1H,15N and31P,15N INEPT spectra) showed the influence of the ring size and conformational effects on the NMR parameters.31P,13C shift‐correlated 2D spectra were further used to measure (including sign determination) and assign31P‐13C coupling constants across one to three bonds in 1‐5. Based on the analysis of the coupling information and the known conformation of 4a, the relative stereochemistry of the diastereomers 4a and b could be derived; further, the comparison of the31P‐13C coupling data of 1‐3 with those of the 4a and b allowed the conformations of these derivatives, which were previously unknown, to be determined. The derived information of the constitution and stereochemistry of 1‐5 gives insight into mechanistic details of the iminophosphine

ISSN:0749-1581    

DOI:10.1002/mrc.1260330110

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractContrary to previous reports, Cl−is visible by35Cl NMR inside human erythrocytes. In spectra run at 49.01 MHz the intracellular chloride has a linewidth at half‐height ofca700 Hz and shows double Lorentzian character. Mn2+was used to relax the extracellular35Cl−to allow the intracellular35Cl−to be seen. The experimental protocol described should allow NMR observation of anion transport rates in human eryth

ISSN:0749-1581    

DOI:10.1002/mrc.1260330111

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY