摘要:

Abstract13C chemical shifts and13CH coupling constants for classical and non‐classical structures of some typical carbonium ions have been calculated by the method of summation over excited states in the INDO approximation using a special parameterization. Comparison of the data obtained with the experimental values shows that the calculation of the chemical shifts and spin‐spin coupling constants is superior to energy calculations, and provides a useful means for the study of the structure of carbonium i

ISSN:0030-4921    

DOI:10.1002/mrc.1270140502

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractParamagnetic NMR shift reagents, Eu(fod)3and Pr(fod)3, have been applied to study the one‐ene conformations of isomeric dienones. The results obtained using various complex formation models are analysed. The preferred model suggests participation of both carbonyl oxygen Ione pairs in binding with the shift reagents. Criteria for the estimation of errors in the determination of the structure parameters of the substrate‐paramagnetic reagent complexes are suggested. The data obtained using NMR shift reagents are consistent with the existence of dienone α,β‐cis‐isomers ass‐cis‐conformers only, with the carbonyl group lying out of the plane of all the other atoms of the molecule. Boths‐cisands‐transconformers occur in dienone

ISSN:0030-4921    

DOI:10.1002/mrc.1270140503

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe stereochemistry in solution of three octathia[2.2.2.2]metacyclophanes has been investigated by means of1H NMR spectroscopy. The results lead to the conclusion that the saddle or crown conformation is preferred for these compounds, depending on the substitution pattern of the constituent aromatic rings.

ISSN:0030-4921    

DOI:10.1002/mrc.1270140504

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe13C chemical shifts of several bicyclic and monocyclic oxonium salts are reported and, in the case of 5‐membered ring unsaturated oxonium salts, compared withab initioand CNDO calculated charges. A prime dependence of the13C shielding on the π charge delocalization effects induced by the Y group is established for the Y‐substituted C‐α carbon; a good correlation of δC‐α vs qπis obtained, using π bond‐order terms. However, contradictory information arises from NMR and theoretical calculations for the C‐ω carbon, which is distant from the Y group. The res

ISSN:0030-4921    

DOI:10.1002/mrc.1270140505

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

Abstract15N and14N NMR spectra show that there is no valence tautomerism involving the nitro group in nitro derivatives of benzofuroxan systems and that theN‐oxide function has a fixed position in the furoxan ring. Carbon chemical shifts of molecules with one, two or three furoxan rings attached to a benzene ring reveal additivity of effects which makes possible a complete and unambiguous assignment of the shift

ISSN:0030-4921    

DOI:10.1002/mrc.1270140506

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of six hydroxybenzenes, all chlorobenzenes, all chlorophenols and eight chlorocatechols are measured and assigned. The additivity of the substituent effects and the usefulness of some corrective parameters are studied with regression analysis. The order of the chemical shifts is most efficiently predicted by the simplest substituent effect model, containing only the direct effects of the substituents, although the 95% confidence limits of the calculated shifts are as high as 5.6 ppm. If the chemical shifts need to be predicted within the measuring errors (approximately 0.05–0.10 ppm, in the present data), the number of necessary corrections is very impractical. The correction parameters are found to be independent of the solvent if no conformational effects are operative. These corrections, or the non‐additivity parameters, are thus theoretically interesting. Approximate1J(CH) couplings are also reported and the additivity of substitution effects on these parameters are discus

ISSN:0030-4921    

DOI:10.1002/mrc.1270140507

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe general correlation between the electron densities and the13C NMR chemical shifts is found to be quite poor in the cases discussed. The non‐additivities of the substituent effects on the chemical shifts and the CNDO/2 electron densities correlate only weakly. However, when the electron densities are made specific to different types of atomic orbitals, theselectrons have a pronounced effect in all the models tested. This is explained by an indirect effect on the 〈1/r3〉 term of thepelectrons. Good correlations are found between the sums of the chemical shifts and the corresponding sums of the substituent charge excesses. The different behaviour of OH and Cl substituents in the additivity of the substituent effects can be explained by their different back‐bonding pro

ISSN:0030-4921    

DOI:10.1002/mrc.1270140508

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe13C resonances of ethidum bromide (1), dimidium bromide (2) and 3,8‐diamino‐5‐methylphenanthridinium chloride (3) in D2O solution have been assigned. Assignments were made using fully coupled spectra, spectra obtained from a selected 180°‐τ‐90° pulse sequence in conjunction with gated irradiation to obtain NOE intensification, selective proton decoupling, chemical shift arguments and by noting the effect of pD on the13C chemical shift

ISSN:0030-4921    

DOI:10.1002/mrc.1270140509

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractIn a heteronuclear13C{1H} selective population inversion13C NMR spectrum a splitting, resulting from a (CH) coupling over more than one bond, can be detected even when no splitting is observed in the single‐frequency13C NMR spectrum. The relationship between the observed splitting, coupling constant and line width is discussed. A method is proposed from which the value of the coupling constant can be estimated, and its application illustrated by the splittings observed in the13C NMR spectra of the mycotoxin, ochratoxi

ISSN:0030-4921    

DOI:10.1002/mrc.1270140510

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

Abstract14N nuclear quadrupole resonance (NQR) spectra of 22 monosubstituted anilines are reported and analyzed in the framework of the Townes and Dailey theory. Satisfactory correlations of the NQR data with both the Hammett σ parameters and thein vitrobiological activities of the corresponding sulfanilamides have been found. The results obtained suggest that the nitrogen lone‐pair orbital is more sensitive than the nitrogen–carbon sigma orbital is to substituent eff

ISSN:0030-4921    

DOI:10.1002/mrc.1270140511

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY