摘要:

AbstractThe principal elements of the chemical shift tensors for the phosphorus atoms in three bis(dialkoxythiophosphoryl) disulfides were determined from both static and magic angle spinning NMR spectra, using the intensities of the peaks in the spinning sidebands relative to those of the central band in the latter method. These studies show that it is possible to deduce a mode of molecular motion in the solid state by analysis of the shielding parameters. Variable‐temperature13C and31P CP MAS NMR of these samples from 190 to 320 K revealed a peculiar motion of the methoxy group and a rigid PSSP backbone for bis(dimethoxythiophosphoryl) disulfide. In addition, these studies confirmed that it is possible to distinguish the different x‐ray crystal structures from the solid‐state NMR

ISSN:0749-1581    

DOI:10.1002/mrc.1260280603

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe application of1H and13C NMR correlations and phase‐sensitive NOESY in the stereochemical assignment of four diastereoisomers of hexacarbonyl{μ‐η4‐[2,4‐dimethyl‐2‐(1‐ethoxy‐2‐propyn‐1‐yl)‐8‐oxabicyclo [3.2.1] octan‐3‐on

ISSN:0749-1581    

DOI:10.1002/mrc.1260280604

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractExperimental and theoretical studies carried out to investigate the influence of strong coupling effects in the spectra generated through the commonly used heteronuclear chemical shift correlation (HETCOR) sequences involving a constant evolution time are reported. It is seen that the spectra generated via such sequences are prone to artifacts of appreciable intensity. Failure to recognize these can result in the misinterpretation of spectral data.

ISSN:0749-1581    

DOI:10.1002/mrc.1260280605

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractSeveral α,β‐diphosphonates with a norbornane or cyclohexane skeleton were prepared, and the31P‐31P coupling constants over three bonds for the ethyl or methyl esters, the acid and anion were obtained from the13C NMR spectra or the13C satellites in the31P NMR spectra. The3J(PP) values cover a range of about 90 Hz and are therefore well suited for conformational and configurational analysis. The dependence of3J(PP) on the dihedral angle is well reflected by an extended Karplus relationship:3J(PP) =A+Bcos φ +Ccos 2φ +Dcos 3φ, with different parameters for the esters, acids and anions. Fortransandgauchearrangements of the α,β‐diphosphonic acids the dependence of the P‐P coupling constants on the degree of titration is given. Investigations of the dependence of3J(PC) on the PCCC dihedral angle show that a good curve fitting is achieved using the Karplus relationship3J(PC) =AA +ABcos φ +Ccos 2φ. A comparison of these curves with published data indicates smaller coupling constants for φ ≈ 0°. The coefficients of the Karplus equation for the3J(PC) values obtained for esters are similar

ISSN:0749-1581    

DOI:10.1002/mrc.1260280606

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractA1H dynamic NMR study of the hindered rotation in 5‐amino‐6‐(N‐methylformamido)‐as‐triazin‐3(2H)‐one was conducted. Signals for two rotamers were observed and their proton chemical shifts were assigned. It was found that the rotamer in which theas‐triazine ring iscisto the formyl hydrogen predominates. The free energies of activation for hindered rotations about the N CHO and C NH2bonds were determined by1H NM

ISSN:0749-1581    

DOI:10.1002/mrc.1260280607

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe1H,13C and31P NMR spectra of [Ru(CH2C6H4CH2)(PMe3)3], which contains a coordinatedo‐xylidene moiety, have been analysed. Parameters such as the geminal coupling in the methylene groups, P,H couplings and the chemical shifts of the quaternary ring carbon atoms all point to a metal‐o‐xylidene binding that is intermediate between σ2,π and π2. Spectral assignment is assisted by P‐H correlation spectroscopy using the COLOC sequence. The best parameter for identifying the bonding mode is the chemical shift for the quaternary aromatic ca

ISSN:0749-1581    

DOI:10.1002/mrc.1260280608

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe13C NMR methyl group multiplet of the [cyclopentadienyltris(trimethylphosphine)iron]+cation was simulated to obtain the sign and magnitude of the phosphorus‐phosphorus coupling constant and the13C/12C isotope effect on the31P chemical shif

ISSN:0749-1581    

DOI:10.1002/mrc.1260280609

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe allenic carotenoid all‐trans‐(3S,5R,6S,3′S,5′R,6′R)‐19′‐butanoyloxyfucoxanthin, isolated from the marine chrysophytePelagococcus subviridis, and its 9′‐cisisomer, obtained in 45% yield on iodine‐catalysed stereomutation, were submitted to a detailed1H and13C NMR analysis. For comparison, all‐trans‐fucoxanthin [(3S,5R,6S3′S,5′R,6′R)‐5,6‐epoxy‐3,3′,5′‐trihydroxy‐6′,7′‐didehydro‐5,6,7,8,5′,6′‐hexahydro‐β,β‐caroten‐8 ‐one‐3′‐acetate] was included in the study. The complete assignments of the 400 MHz1H NMR spectra and of the 100.6 MHz13C NMR spectra, including the stereochemistry, were possible by application of two‐dimensional1H,1H chemical shift correlated spectroscopy (2D COSY), 1D and 2D total correlation spectroscopy (TOCSY, HOHAHA), rotating‐frame nuclear Overhauser spectroscopy (ROESY, CAMELSPIN) and1H‐detected one‐bond (with and without13C decoupling) and multiple‐bond1H,13C‐correlated 2D spectroscopy. The 9′‐transto 9′‐cisstereomutation was unequivocally proved for 19′‐butanoyloxyfucoxanthin, mainly by 1D and 2D ROESY experiments

ISSN:0749-1581    

DOI:10.1002/mrc.1260280610

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of several diterpenic derivatives having the podocarpane and cassane skeleton were recorded and interpreted. The most significant effects due to substituent orientation, B/C ring junction stereochemistry and conformational changes are briefly discussed.

ISSN:0749-1581    

DOI:10.1002/mrc.1260280611

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

Abstract13C NMR spin–lattice relaxation times (T1s) and nuclear Overhauser enhancements (NOE's) were measured for a series of clinically used tricyclic antidepressants (TCAs), imipramine (1), amitriptyline (2), doxepin (3) and dothiepin (4), at two magnetic field strengths (corresponding to13C frequencies of 75 and 100 MHz). The measurements were carried out at a range of solution concentrations in CDCI3and D2O in order to determine the factors that influence overall and internal molecular dynamics in these systems. Both the hydrochloride salts and free bases were examined. For solutions in CDCI3 over a range of concentrations, or for low‐concentration (0.03 M) solutions in D2O,T1and NOE measurements were independent of magnetic field strength, indicating that motion of the TCAs was in the ‘extreme narrowing limit.’ In contrast, for 0.3 M solutions of the hydrochloride salts in D2O,T1and NOE measurements were field dependent, indicating the presence of significantly slower molecular mobility. It is proposed that micelles are present at this concentration and are responsible for reduced overall tumbling of the TCAs. Several degrees of internal motion were detected by the relaxation andT1measurements, viz. rapid flexing motion of the benzylic bridging carbons in the central seven‐membered ring and segmental motion of the side‐chain. From an examination of the effect of solvent, concentration and protonation state of the side‐chain on the latter motion, it was possible to derive information on side‐chain conformations a

ISSN:0749-1581    

DOI:10.1002/mrc.1260280612

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY