摘要:

Abstract2DJ—δ selective INEPT experiments were used to measure long‐range13C,1H coupling constants for the macrolide antibiotics roxithromycin, erythromycin and their metabolites, RU 39001 and erythralosamine, respectively. The 2DJ—δ selective INEPT experiment was performed using selective excitation by a DANTE pulse train. In some cases, to avoid truncation problems in thet1domain, treatment of the data using a linear prediction method was adopted. Dihedral angles for the glycosidic bonds and the erythronolid unit were deduced from a Karplus‐type equation for conformational study. The apparent equilibrium between different conformers is discussed by comparison of experimental results and theoretical calculations by molecular

ISSN:0749-1581    

DOI:10.1002/mrc.1260320102

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractDeuterium NMR and relaxation data are presented to investigate the state of β‐cyclodextrin in aqueous solution and to derive dynamic parameters for inclusion complexes. Labelled host and guest molecules were used, and dedicated pulse sequences are proposed for improving the deuterium spectra in terms of reduction of artifacts and of solvent peak(s) and also in terms of total duration of the experiments. This technique was used to investigate the state of β‐cyclodextrin in aqueous solution and to derive important information regarding the degree of dynamic coupling between host and guest in inclusion comp

ISSN:0749-1581    

DOI:10.1002/mrc.1260320103

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractIn H,H COSY spectra of rigid cyclic terpenes, many long‐range couplings can be observed. The coupled nuclei are connected either by a zig‐zag coupling path or they are close in space. The latter are called ‘through‐space’ coupling. A certain stereospecific relationship between the coupling partners is necessary. This phenomenon is in accordance with the theoretical exp

ISSN:0749-1581    

DOI:10.1002/mrc.1260320104

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe molecular mobility and dehydration reaction oftert‐butyl alcohol, selectively deuteriated in the methyl groups (t‐BuOH[2 –2H9], dTBA), absorbed on H‐ZSM‐5 zeolite was studied using2H NMR spectroscopy. At 173–298 K two modes of fast anisotropic motion were observed for the adsorbed alcohol: rotation of CD3groups around the CC bonds and rotation of the entire (CD3)3C fragment around the CO bond. The influence of the walls of the H‐ZSM‐5 channels on the geometry of adsorbed dTBA is small, the increase in the CD3CO angle not exceeding 2.7 ± 1.2° compared with the same angle in solid dTBA. This is explained by location of the alcohol molecules at channel intersections of the zeolite, whose dimensions exceed those of the dTBA molecule. The lifetime of the dTBA molecule at these adsorption sites exceeds 1 × 10−5s. The observed reaction products are deuteriated water with an unusual2H NMR lineshape and two types of butene oligomers: less mobile species with the lineshape typical of solid‐state2H NMR and more mobile species with a liquid‐like lineshape. The number of more mobile species increases with increase in temperature. In addition,2H NMR indicates the presence oftert‐butyl groups in the reaction products. For oligomers with a liquid‐like lineshape, the diffusion coefficientDis 3 × 10−13m2s−1at 373 K, whereas for oligomers with a solid‐like lineshapeD≪ 5 × 10−14m2s−1at 173‐373 K. The diffusion coefficient for thet‐BuOH molecule was estimated asD

ISSN:0749-1581    

DOI:10.1002/mrc.1260320105

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNMR nutation and quadrupole echo experiments were used to determine the quadrupole frequency (ωQ) of87Rb (I= 3/2) in a single crystal of RbCaF3. Since RbCaF3has a cubic unit cell above 195 K, there is no second‐order quadrupole shift and the spectrum is rather featureless. By fitting the response of87Rb, as a function of pulse duration, to the predicted response we were able to determine that the average ωQ/2π = 4.5 kHz in this sample. Discrepancies in the agreement between the theory and the experiment for the echo response were attributed to differential relaxation of the central and satellite transit

ISSN:0749-1581    

DOI:10.1002/mrc.1260320106

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of 132(R)‐methoxychlorophyllawere assigned utilizing the two‐dimensional1H‐detected heteronuclear one‐bond (HMQC) and multiple‐bond (HMBC) correlation techniques. The protons and carbons of the macrocycle and its short side‐chains could be completely assigned using the HMQC and HMBC data in concert. These techniques were also valuable in achieving assignments for the phytyl chain, which were previously incomplete. The proton and carbon assignments of the P1‐CH2, P2‐CH, P4‐CH2and P15‐CH groups and those of all methyl groups of the phytyl chain could be established by the coupling patterns and by the combined information obtained from the HMQC and HMBC connectivities. Fairly unambiguous proton and carbon assignments were also obtained for the P6‐CH2, P7‐CH, P9‐CH2, P11‐CH and P14‐CH2groups. The sensitivity of the HMQC and HMBC techniques is good, making it possible to achieve the spectral assignments under high dilution and monomeric conditions. This was considered to be of paramount importance in the structural analysis of chlorophylls and related compounds, which are difficult to prepare in adequate amounts and purity because of their lability and which show a strong aggregation tendency at higher concentr

ISSN:0749-1581    

DOI:10.1002/mrc.1260320107

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe natural hybrid orbitals of halogen atoms in various halogen‐substituted alkanes and benzenes have been calculated by the Fenske–Hall MO SCF method and natural hybrid orbital theory. Four consistent parametersi, s, dand π are derived to describe the nuclear quadrupole coupling constant (QCC) of the halogen isotopes35Cl,81Br and127I, with modification by the asymmetry parameter η. A semi‐empirical expression is proposed from a different point

ISSN:0749-1581    

DOI:10.1002/mrc.1260320108

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe1H,13C and29Si NMR spectral characteristics of β‐silylated silyl enol ethers were determined.nJ(Si, H) measurements (2

ISSN:0749-1581    

DOI:10.1002/mrc.1260320109

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNatural abundance17O NMR data for seven aliphatic, nine cyclic and thirteen aromaticN‐nitrosamines, recorded at room temperature in acetonitrile, are reported. Differences in chemical shifts among and within the three groups are discussed in terms of electronic and steric effects. The σ+value for theN‐nitrosamine group was estimated. A comparison between amides andN‐nitrosamines wa

ISSN:0749-1581    

DOI:10.1002/mrc.1260320110

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractFivepara‐fluorobenzene derivatives having a CHCR2or a CHNR group were prepared and their1H and19F NMR spectra in acetone‐d6were analysed. The6J(Hα,F) and4J(Hα,H) couplings of the nitrogen derivatives fall between those of the carbon and oxygen derivatives: the electronegativity of the side‐chain β‐atom seems to have a prominent role in the spin information transmission. The6J(Hα,F) and4(Hα,H) couplings indicate that the nitrogen derivatives are rigidly planar whereas the carbon deriva

ISSN:0749-1581    

DOI:10.1002/mrc.1260320111

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY