摘要:

AbstractThe assignment of the proton and carbon signals and conformations of substituted 5,6‐dihydro‐4H‐1,3‐oxazines were determined by the combination of1H,13C, COSY and HETCOR spectr

ISSN:0749-1581    

DOI:10.1002/mrc.1260310702

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe long‐range coupling constant4J(31P, C, S, C,1H) was measured in several diethyl α‐methylthio‐substituted phosphonates and their analogues. A dependence of the4Jcoupling on the substituent electronegativity was ob

ISSN:0749-1581    

DOI:10.1002/mrc.1260310703

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractIn order to determine the nature and the structure of polymers formed by condensation of alkoxysilanes, a two‐dimensional INEPT double quantum filtered COSY NMR experiment was developed to observe29Si29Si correlations at29Si natural abundance. This experiment was tested on a mixture containing a trimer, [(CH3)3SiO]2Si(CH3)2, and a tetramer, [(CH3)3SiOSi(CH3)2]2O. This 2D INEPT DQF COSY experiment was then used to investigate the nature and the structure of the polymers which are formed in the early stages of the condensation reaction of diethoxydimethylsilane (DEDMS) in a DEDMS–water mixture containing a small amount of water at low pH

ISSN:0749-1581    

DOI:10.1002/mrc.1260310704

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe combination of high‐performance liquid chromatography (HPLC) and ESR spectrometry was used to isolate the free radicals produced by the reaction of a Grignard reagent with 15 substituted α‐Phenyl‐N‐tert‐butylnitrone. Long‐range hyperfine splitting constants (hfsc) were obtained by the resolution enhancement method. Linear correlation studies between hfsc and Hammett σpconstants are reported. Dual‐parameter correlations using σRand σIwere also studied. The mass spectra for the HPLC‐isolated spin adducts and their fragmentation pa

ISSN:0749-1581    

DOI:10.1002/mrc.1260310705

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe1H CW off‐resonance decoupled13C NMR spectra of (E)‐ and (Z)‐cycloalkenes (C5C12) were measured. The higher order13C NMR multiplets obtained for the unsaturated carbons allow the determination of the vicinal1H,1H coupling constant between the vinylic protons and thus the assignment of the configuration of the CH2CHCHCH

ISSN:0749-1581    

DOI:10.1002/mrc.1260310706

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractEleven substituted 2‐diethylaminomethylphenolN‐oxides were studied in CDCl3solutions by1H and13C NMR spectroscopy. The1H chemical shifts of the intramolecular hydrogen‐bonded proton and the Δ14values obtained from the13C signals were considered as a function of the pKavalues of the parent phenols. The1H chemical shift of the hydrogen‐bonded proton shows a maximum at pKa≈ 7. This result agrees well with the turning point of the curve if Δ14is plotted as a function of the pKaof the parent phenols. All these results agree well with recently obtained Fourier transform IR results. With the system with the strongest hydrogen bond (pKa≈ 7) a broad, flat, single‐minimum proton potential or a double‐minimum proton potential with a small barrier is present. With this system the deshielding of the proton in the intramolecular hydrogen

ISSN:0749-1581    

DOI:10.1002/mrc.1260310707

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractComplete1H and13C NMR resonance assignments were carried out for six stereoisomeric 6,7‐glycol derivatives of deoxycholic acid as their methyl esters (four being in the 5β‐series and two in the 5α‐series). In addition to conventional 1D NMR methods, 2D shift‐correlated NMR techniques (1H1H COSY,1H1H NOESY and1H13C HETCOR) were used for the signal assignments. Several1H and13C resonances have been reassigned from those previously reported. Substituent effects of the 6,7‐glycol moieties on the proton and carbon resonances were clarified and used in the structural elucidation o

ISSN:0749-1581    

DOI:10.1002/mrc.1260310708

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe temperature and concentration dépendences of the chemical shift of aqueous selenous acid were studied in order to establish a precise relationship between the shift of this convenient reference and that of dimethyl selenide. The chemical shift of saturated H2SeO3in H2O on the Me2Se shift scale at 20°C is 1300.0 ppm and its temperature coefficient is 0.094 ppm K−1. The relationships to the chemical shifts of Me2Se in CDCl3and SeO2in D2O are also discussed. The results permit the correlation of77Se NMR shifts from several sour

ISSN:0749-1581    

DOI:10.1002/mrc.1260310709

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractComposite pulses that compensate for resonance offset and electric field gradient inhomogeneity are proposed for broadband excitation of pure nuclear quadrupole resonance systems in powders. The excitation band width of the composite pulse sequences was obtained with a numerical calculation procedure and confirmed by35Cl experimental spectra of powdered NaClO3.

ISSN:0749-1581    

DOI:10.1002/mrc.1260310710

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractIn order to clarify the special properties of the aryl‐bound nitramino substituent NRNO2(R = H, CH3),13C and15N NMR spectra of six nitraminobenzenes and nine nitraminopyridines were measured in DMSO‐d6and their chemical shifts assigned.1H NMR chemical shifts and spin‐spin coupling constants of all the compounds were also determined. In contrast to the behaviour of nitropyridines or ‐benzenes studied previously, most of the present compounds gave very broad17O NMR lines even at elevated temperatures and their17O NMR data were not useful for any reliable conc

ISSN:0749-1581    

DOI:10.1002/mrc.1260310711

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY