摘要:

Abstract15N NMR chemical shifts were measured for a series of substituted 5‐amino‐1,2,4‐triazoles. The assignment of isomeric structures agrees with earlier results obtained with the use of proton‐coupled

ISSN:0749-1581    

DOI:10.1002/mrc.1260270102

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe 360 MHz1H and 15 MHz13C NMR spectra of 2, 2′‐biquinoline, 2,3′‐biquinoline and 6,6′‐dimethyl‐2,3′‐biquinoline are presented and assigned. The diamagnetic anisotropic effect of the neighbouring aromatic ring (Dc) and the electrostatic field effect of the nitrogen lone pair (DN) result in characteristic deshielding effects in the1H NMR spectra of these compounds. The characteristic chemical shift differences (ΔHand Δc) between nuclei at the corresponding position but on different rings is proposed as an additional assignment aid for the1H and13C NMR spectra of unsymmetric biaryls and biheteroaryls. The reaction of quinoline and of 6‐methylquinoline with sodium gives

ISSN:0749-1581    

DOI:10.1002/mrc.1260270103

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of several fluorine‐substituted polycyclic aromatic hydrocarbons in which fluorine projects into a bay region were studied. Both protons and carbons of the sterically opposed CH bond show anomalously large F‐induced shifts and couplings to fluorine. The magnitudes of the couplings (particularly the four‐bond CF couplings which average 26 Hz) indicate a large through‐space contribution due to direct overlap between fluorine and CH bond orbitals, whereas the F‐induced shifts seem more likely to stem from diamagnetic anisotropy rather than F‐induced CH bond p

ISSN:0749-1581    

DOI:10.1002/mrc.1260270104

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe application of various methods of data processing of a raw, untreated free induction decay (FID) to improve the quality of noisy and overcrowded spectra is shown. The use of complex interpolation of fragments of a typical31P NMR spectrum of humic substances from forest soil in D2O, combined with two‐stage apodization of the FID, results in better defined signals and a higher accuracy of the integration of signals partially overlapped in the initial spectrum. Convolution difference resolution enhancement was used to enhance the spectral resolution of overlapped orthophosphate ion and orthophosphate monoester signals, while the noise was attenuated by a decreasing exponential.An attempt to detect carbon signals buried in the noise by applying a rapidly decaying exponential (line broadening of 10 or 50 Hz) to a noisy FID, and the use of resolution enhancement, are also described for the13C NMR signals from soil extract

ISSN:0749-1581    

DOI:10.1002/mrc.1260270105

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractCarbon‐13 NMR spectra are reported for 63 substituted benzonitriles in deuteriochloroform or in its mixture with dimethyl sulphoxide‐d6. The substituent‐induced chemical shifts (SCS) of the CN carbon correlate well with dual substituent parameters (DSP) in theparaseries but poorly in themetaseries, whichever parameters are used. The DSP treatment was found to be inferior to principal component analysis (PCA), using as a probe 29 sets of literature data on α,β‐unsaturated benzene derivatives. Whereas one component is sufficient formetaderivatives, two terms are needed forparaderivatives, which are different for the α‐ and β‐positions. The constants derived by PCA could be in principle used to predict further SCS, but their scope must be

ISSN:0749-1581    

DOI:10.1002/mrc.1260270106

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe fully coupled (FUCOUP) correlation experiment was used to analyze conformation and stereochemistry on two dissimilar compounds, strychnine and camphor. This experiment detects the vicinal coupling between hydrogens and carbons, and the magnitude of this coupling is appraised by the presence or absence of cross‐peaks in the spectrum. This correlates with a first‐order approximation of the Karplus torsional angle relationship, although angles near 45° and 135° are not useful. The FUCOUP experiment works better than other related methods because it has no delays that modify the signal intensity of the cou

ISSN:0749-1581    

DOI:10.1002/mrc.1260270107

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe 60 and 100 MHz1H NMR spectra of γ‐butyrolactone were analysed in detail. The best set of coupling values (Hz ± 0.03) is3J ABc= 7.86,3J ABt= 6.27,3J BCc= 9.52,3J BCt= 6.86,4J ACc+4J ACt= −0.18,2JA−2JB= 3.89 and2JB−2JC= 4.86 (A, B and C refer to α, β and γ protons, with respect to the ring oxygen, andcandtmean the same and opposite side of the ring, respectively). The3Jvalues support the conclusion that the molecule is interconverting between two equivalent conformations of near envelope type with the β‐carbon out of the mean plane defin

ISSN:0749-1581    

DOI:10.1002/mrc.1260270108

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

Abstract1H high‐resolution NMR spectra of polycrystalline alkali trihydrogen selenites were measured at 270 MHz using the combination of a multiple‐pulse sequence and magic angle sample spinning. Good resolution of the separate1H NMR lines belonging to different hydrogen bonds in these crystals was obtained. Correlations between the measured average values of the chemical shift tensor and the parameters characterizing hydrogen bond [R(O…O) andR(H…O)] distances and the deuteron quadrupolar coupling constante2qQ/hare presented. These correlations are found to be linear, with high correlation coefficients for the ordered protons. The possibilities of designating disordered protons on finding large deviations from the correlations for ordered protons are di

ISSN:0749-1581    

DOI:10.1002/mrc.1260270109

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractAs an electron donor solvent, propylene oxide (PO) forms a hydrogen bond with water in their binary mixture. The repulsion produced by the electrostatic field from the PO…HOH hydrogen bond forces the protons and methyl group of PO to bend away from the O group and results in the approach of these protons into the plane of the three‐membered ring. Consequently, they experience a stronger paramagnetic field from the ring current and their1H resonances shift to a lower field. The changes of the HCH angle and HCCH dihedral angles of PO in water cause the geminal coupling constant and the vicinalciscoupling constant to decrease and the vicinaltranscoupling con

ISSN:0749-1581    

DOI:10.1002/mrc.1260270110

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

Abstract13C spin‐lattice relaxation times (T1) were measured for resolved carbons in flexible‐chain molecules consisting of a hydrocarbon chain attached to benzophenone at theparaposition. Effective correlation times,teff, were determined fromT1data and used to discuss the motional features of these molecules as a function of chain length, chain unsaturation and type of linkage by which the chain is attached to the benzophenone moiety. Of particular interest is the finding that the overall motion and chain mobility are greatly affected by the introduction of an unsaturated bond in the chain, depending on its configuration and location in the hydrocarbon t

ISSN:0749-1581    

DOI:10.1002/mrc.1260270111

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY