摘要:

AbstractAn approach to spinning sideband (SSB) separation of protonated and non‐protonated carbons in slow spinning conditions via dipolar dephasing is proposed. This method offers two features: SSB spectral simplification, which greatly reduces the overlaps encountered in a usual SSB spectrum, and spectral distinction of overlapped resonances for protonated and non‐protonated carbons. The13C chemical shift anisotropies of the 20 amino acids as polycrystalline powdered solids were completely measured with the SSB intensity analyses as an application of the suggested appro

ISSN:0749-1581    

DOI:10.1002/mrc.1260310802

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractESR spectra of bipyridyl(Bipy) adducts of copper(II) salicylhydroxamates were obtained at room and liquid nitrogen temperatures in polycrystalline samples. The bonding ability of Bipy is discussed on the basis of N‐superhyperfine coupling (N‐Shf) while the magnitude of CuL bonding is discussed on the basis of ESR parameters. The room temperature magnetic moment values indicated tetragonal distortion. The nature of distortion is also discussed on the basis of N‐Shf c

ISSN:0749-1581    

DOI:10.1002/mrc.1260310803

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

Abstract7Li,23Na and13C solid‐state NMR spectroscopy under static and magic angle spinning conditions was used to study the salt complexes of lithium chloride, lithium bromide, lithium perchlorate and lithium nitrate with 12‐crown‐4 and of sodium nitrate with 15‐crown‐5, Structural and dynamic features of the compounds are discussed, focusing on the quadrupolar interaction and temperature‐dependen

ISSN:0749-1581    

DOI:10.1002/mrc.1260310804

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractA wide variety of push–pull alkenes were studied by means of variable‐temperature1H and13C NMR spectroscopy with respect to the configuration/conformation and the barriers to rotation about partial CC and CN double bonds. For the assignment of the13C NMR spectra especially the semi‐selective INEPT pulse sequence and an incremental system for estimating the13C chemical shift values of aromatic carbon atoms proved useful. The influence of thioether, sulphone and sulphoxide moieties in the acceptor part of the push–pull system on the π‐electron distribution is critica

ISSN:0749-1581    

DOI:10.1002/mrc.1260310805

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractCorrelatedab initiocalculations of the dependences of the proton–proton spin–spin coupling constantJ(H1,H2) in methane with the variation of the H1CH2interbond angle are reported. The other coupling constants, includingJ(C, H), were simultaneously calculated. The coupling constantsJ(H1, H2) andJ(C, H1) increase nearly linearly with the opening of the interbond angle whereasJ(H2, H3) andJ(C, H3) decrease.J(H3, H4) is only very slightly affected. The changes are due almost solely to changes in the Fermi contact term. The angular dependence is slightly larger at the SCF level of calculation than at the correlated level. The change in the geminal coupling constantJ(H1, H2) with respect to equilibrium geometry is given to within 0.025 Hz by ΔJ(H1, H2) (Hz) = 41.57 sin α12− 8.90 sin2α12, where α12is the increase in the interbond angle with respect to equilibrium ( −

ISSN:0749-1581    

DOI:10.1002/mrc.1260310806

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractHydrogen and carbon‐13 NMR chemical shifts of five complexes of 1,8‐bis(dimethylamino)naphthalene with strong acids were measured in acetonitrile‐d3and nitromethane‐d3and identified by 2D, NOE difference and long‐range enhanced COSY spectra. The assignments of the resonances corresponding to H‐2,7, H‐4,5, C‐3,6 and C‐4,5 obtained in this study differ from those re

ISSN:0749-1581    

DOI:10.1002/mrc.1260310807

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractInclusion complex formation between the explosive molecules of the nitramine type, RDX, HMX and TNAZ, and cyclodextrins (α, β and γ) was studied in aqueous solution by means of1H spin–lattice relaxation time (T1) measurements. The results show that nitramines bind to cyclodextrins in solution; RDX and HMX bind most strongly to γ‐cyclodextrin whereas TNAZ binds most strongly to β‐cyclodextrin. The dynamic coupling coefficient and dissociation constant were determined for the complex of TNAZ with β‐cyclodextrin. The values obtained suggest that TNAZ forms a relatively weak complex with β‐cyclodextrin (Kd= 1.8 × 10−2M) that displays considerable motion in the complex with respect to cyclodextrin (coupling coefficient = 0.23). This method of using1HT1measurements for characterizing complex formation in solution, while limited to guest molecules containing a pair of protons having a fixed internuclear distance, is shown to be useful when complexation‐induced chemical shifts are too sm

ISSN:0749-1581    

DOI:10.1002/mrc.1260310808

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe77Se,13C and1H NMR spectra of 57 mostly new compounds with phenylselenenyl groups attached to acyclic alkanes, alkenes and phenylalkanes and of 10 corresponding selenoxides are reported. Substituent effects on the chemical shifts of these nuclei were determined and are discussed in terms of the conformation and configuration. The results suggest that, in contrast to PhSeCCSePh fragments, CCCSe chains prefer agauchec

ISSN:0749-1581    

DOI:10.1002/mrc.1260310809

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractIn concentrated alkaline sodium silicate solutions a consistent decrease in the amount of silicate monomerQ0, end‐groups Q1, cyclic trimer Q cyc2groups and middle groups Q2, and also branching groups in ring formationsQ cyc3, is observed with increasing molar ratio of SiO2to Na2O (RM), whereas for branching groups Q3and cross‐linking groups Q4a consistent increase is found. The interest of this work is particularly focused on the Q4region, which may indicate the formation of colloidal silicate particles. For this region the29Si background signal from the NMR probe and the glass tube can cause problems, so the subtraction technique was used. Spin‐lattice relaxation times, not previously reported for silicate solutions of concentrations and molar ratios as high as those studied here, are given for all structural units, including Q4. It was found that sodium silicate solutions ofRM = 2.0 do contain a Q4region when they are extremely highly concentrated in SiO2(38 wt% SiO2

ISSN:0749-1581    

DOI:10.1002/mrc.1260310810

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

Abstract19F NMR chemical shifts and coupling constants are given for a series of aryl (phenyl, naphthyl and phenanthryl) substituted trifluorovinyls and (E)‐ and (Z)‐perfluoropropenyls. The relationship between the19F NMR chemical shifts and the configurational orientation of the perfluoroalkenyl substituents is discus

ISSN:0749-1581    

DOI:10.1002/mrc.1260310811

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY