摘要:

AbstractThe conformational preferences in solution of eight new open‐chain and cyclic aromatic sulphides containing pyridine or 1,3,4‐thiadiazole units have been investigated, parallel to those of some structurally related phenyl sulphides, by means of1H NMR spectroscopy. The results obtained have shown that replacement of phenyl by the pyridyl or the 1,3,4‐thiadiazolyl moieties induces slightly different propeller arrangements, ascribed to the higher conjugative tendency of both electron‐deficient heteroaromatic rings, in all open‐chain mixed sulphides, in opposition to the skew arrangements observed for phenyl sulphide derivatives. No prominent differences have been found for cyclic sulphides, which preferentially adopt the sterically unhindered saddle shape con

ISSN:0030-4921    

DOI:10.1002/mrc.1270160102

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe structure of the bispyridinium oximes, toxogonin, HS‐3, HS‐6 and HI‐6, used as antidotes in organophosphorus poisoning, is confirmed by13C NMR spectroscopy. The13C NMR spectra of the corresponding monopyridinium precursors substantiate the signal assignment in the bispyridinium oxime spectra. In all oximes studied the hydroxyiminomethyl group (CHNOH) exists in thesynconfiguration. The13C signal differences also readily allow analysis of binary mixtures of the oximes and provide an easy method for monitoring thei

ISSN:0030-4921    

DOI:10.1002/mrc.1270160103

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractAnionic EDTA complexes of Pr(III) and Eu(III) produce downfield and upfield shifts, respectively, of the NH resonances of amidinium ions, RC(NH2)2+. These LnEDTA−‐induced shifts arise through the formation of weak ion pairs. Results for the acetamidinium ion show that Hz, the high field NH, experiences a greater shift than HE. This result confirms the expectation that in the ion pair the anionic shift reagent approaches closer to Hz. Thus LnEDTA−‐induced shifts can be used to assign NH peaks of amidinium ions. Such shifts are then used to assign the low field NH peak of the benzamidinium ion to HE, whereas the low field NH peaks of the azoisobutyramidinium ion and formamidinesulfinic acid are assigne

ISSN:0030-4921    

DOI:10.1002/mrc.1270160104

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe77Se chemical shifts of 79 mono‐ or disubstituted benzo[b]selenophenes are reported. The results in the 2‐ and 3‐substituted derivatives closely parallel those previously obtained in the corresponding selenophenes. The measured parameters also correlate well with those measured in benzo[b]tellurophenes. The125Te and77Se chalcogen nuclei appear to be much more sensitive to substituent effects than the more classical nuclei. The effects of Cr(acac)3, Eu(dpm)3and concentration on the77Se NMR spectra are briefly disc

ISSN:0030-4921    

DOI:10.1002/mrc.1270160105

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

Abstract15N chemical shifts of 3‐methyl‐1‐phenylpyrazole‐4,5‐dione 4‐phenylhydrazone (1), 4‐hydroxyazobenzene (2), 2‐hydroxy‐5‐tert‐butylazobenzene (3) and 1‐phenylazo‐2‐naphthol (4), monolabelled with15N at α‐(compounds prepared from15N‐aniline) and β‐positions (compounds prepared from Na15NO2), have been measured and the temperature dependence of these chemical shifts followed between 240 and 360 K. For 4, representing a mixture of the azo and hydrazone forms, the hydrazone content has been calculated from the15N chemical shifts of both nitrogen atoms at various temperatures. The two

ISSN:0030-4921    

DOI:10.1002/mrc.1270160106

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of 29 highly oxygenated C, steroids with the withanolide skeleton, 24 of which are naturally occurring substances or acetates thereof, were recorded and the carbon signals fully assigned. The shifts of the heavily functionalized A/B ring system can serve as a ‘fingerprint’ for the different substitution patterns. A study of the effects of hydroxyl substitution in the ring D/side chain part of the molecules leads to conformational information, including preferred rotamers around the 17—20 and 20—22 bonds. Systems with both 17α‐ and 17β‐oriented side chains are

ISSN:0030-4921    

DOI:10.1002/mrc.1270160107

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe19F chemical shifts of a series of bridgehead fluorides are reported. It is found that, contrary to earlier conclusions based on a limited number of substrates, the fluorine shifts occur randomly.

ISSN:0030-4921    

DOI:10.1002/mrc.1270160108

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractThe proton nuclear magnetic resonance spectra of benzo[b]‐furan, ‐thiophene and ‐selenophene oriented in a potassium laurate lyotropic liquid crystal have been analyzed. Geometrical information has been obtained and compared to previous thermotropic results and various hypothetical m

ISSN:0030-4921    

DOI:10.1002/mrc.1270160109

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractIt is shown that the γαeffects of hetero substituents on the13C chemical shift (γαSCS) are enlarged by +2 to +5 ppm by substituting the α‐hydrogen atom by any group or atom (e.g. CH3, OR, F, Cl, Br). The same is encountered when the axial γ‐hydrogen is replaced by CH3, OH or F. If, however, the substituting atom at the γα‐carbon atom is a higher‐row halogen (Cl or Br), diamagnetic γαSCS for this signal are observed which may even exceed those for unsubstituted γα‐carbon atoms. The removal of a 1,3‐diaxial hydrogen‐hydrogen interaction and the existence of a still unspecified ‘heavy halogen effect’–both diamagnetic contributions to the γγSCS of hetero substituents–are responsible for these findings. Methyl groups do not behave like hetero sub

ISSN:0030-4921    

DOI:10.1002/mrc.1270160110

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY

摘要:

AbstractN,N‐diisopropylamides and ‐thioamides show hindered rotation around the NCH bonds, and the presence of mixtures of conformational isomers can be demonstrated at temperatures below 273 K in solution.1H and13C NMR spectra of these conformers are measured and assigned. The13C data serve to study through‐space effects on13C chemical shifts, which strongly depend on the conformations of the isopropyl groups. For amides, a through‐space shielding of theN‐methine carbons is found to exist only for conformers in which the methine hydrogen atom is spatially close to the oxygen atom. Chemical shift differences between amides and thioamides can be rationalized in terms of through‐bond and through‐space contributions, and serve for a better understanding of the shift differences inN,N‐dialkylamide

ISSN:0030-4921    

DOI:10.1002/mrc.1270160111

出版商:John Wiley&Sons Limited    

年代:1981

数据来源: WILEY