摘要:

AbstractThe barriers to partial rotation around the central single bond in chiral dienes\documentclass{article}\pagestyle{empty}\begin{document}${\rm HOCMe}_{\rm 2} \rlap{--} ({\rm CCl =\!= CCl\rlap{--})}_{\rm 2} {\rm X}$\end{document}have been determined by coalescence of either1H NMR signals (X = CH2OCH3) or13C NMR signals (X = H). In the presence of the optically active shift reagent (+) − Eu(hfbc)3all1H signals were split at temperatures where the interconversion of enantiomers is slow. The temperature dependence of these spectra also yielded free activation enthalpies for the enantiomerizations which were in agreement with the ones obtained without Eu(hfbc)3. The assignment of the four methyl resonances appearing in the presence of (+) − Eu(hfbc)3at low temperature was possible by gradually increasing the rate of enantiomerization or gradually replacing the optically active auxiliary compound by the racemic

ISSN:0030-4921    

DOI:10.1002/mrc.1270111002

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

AbstractSelf‐consistent perturbation calculations within the INDO framework are reported for 6315N13C coupling constants. Examples are presented for which each of the contact, orbital and dipolar terms provides the dominant contribution to the observed coupling constant. In general, good agreement with the experimental data is obtained when the integral productsSN2(O)SC2(O) and 〈r−3〉N〈r−3〉Ctake the values 14.480 au−6and 2.446 au−6for1J(15N13C), and the corresponding values of 10.444 au−6and 17.664 au−6for1J(15N13C). All 19 of the1J(15N13C) couplings considered are pred

ISSN:0030-4921    

DOI:10.1002/mrc.1270111003

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

AbstractUne série de mérocyanines α‐oxo benzimidazoliniques diversement substituées sur la partie ‘phénolate’ et possédant une chaǐne grasse sur l'un des azotes hétérocycliques, a été étudiée en RMN du carbone‐ 13. Des substituants donneurs d'électrons provoquent une augmentation de la densité électronique sur le carbone méthinique C‐3 et une augmentation de l'alternance de la distribution de charge sur le pont diméthinique 3,4. Corrélativement un déplacement bathochrome de la transition électronique de plus basse énergie est observé. Par ailleurs, l'apparition de la résonance à champ faible du proton méthinique H‐3 semble due à une interaction spécifique intervenant entre ce proton et l'atome d'oxygène ‘phénolate’, ce qui suppose l'existence d'une config

ISSN:0030-4921    

DOI:10.1002/mrc.1270111004

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

AbstractThe group [(CH3)3Si]2CH is effectively bulkier than the (CH3)3C group in inhibiting rotation about the PC bond in R2PCI compounds. In phosphonamidous chlorides, RP(CI)NR2′, increasing the bulk of the groups at nitrogen, e.g., from CH3to (CH3)2CH to (CH3)3Si, increases the rotational barriers about the PN bond; however, changing R from (CH3)3C to [(CH3)3Si]2CH increases the barrier, which is a reversal of the trend earlier observed. It is suggested that these very bulky silylated groups represent limiting cases of steric interferenc

ISSN:0030-4921    

DOI:10.1002/mrc.1270111005

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

AbstractThe feasibility of the application of selective13C{1H} nuclear Overhauser effect (NOE) measurements to organic structural analysis in13C NMR spectroscopy has been investigated at 25 MHz using citraconic anhydride and the methyl ester of pentalenolactone as model compounds. This selective13C{1H} NOE technique with single frequency low‐power1H irradiation should find wide application in the structural elucidation of organic compounds, especially for the reliable assignment of quaternary carbon si

ISSN:0030-4921    

DOI:10.1002/mrc.1270111006

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

AbstractNous avons montré que les produits obtenus lors de la quaternisation du thiazolo[3,2‐d]tétrazole, et de deux de ses dérivés, phényl‐3 thiazolo[3,2‐d]tétrazole et tétrazolo[5,1‐b]benzothiazole, sont des sels de tétrazolium. Nous avons discuté des effets dus à la quaternisation en fonction des résulta

ISSN:0030-4921    

DOI:10.1002/mrc.1270111007

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

Abstract15N chemical shifts of theZandEisomers of twenty‐two ketoximes and fourteen aldoximes have been determined at the natural‐abundance level of15N, using Fourier transform methods. The influences of π delocalization, methyl substituents and solute concentration on the oxime nitrogen shielding have been determined. The15N shifts for oximes of several cycloalkanones have been measured and the influence of ring size on the chemical shifts is discu

ISSN:0030-4921    

DOI:10.1002/mrc.1270111008

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

AbstractCarbon‐13 NMR spectra of several alkyl‐substituted indenes have been assigned and analysed. For structures having an alkyl substituent in the C‐2 position an increased shielding was observed for the remote conjugated positions C‐4 and C‐6, an alternating trend similar to that found for the 2‐cycloaminoindenes. The hyperconjugative behaviour was slightly more pronounced for the methyl group compared with an isopropyl ortert‐butyl substituent, a fact which supports a model where CH σ–π interactions are more efficient than those

ISSN:0030-4921    

DOI:10.1002/mrc.1270111009

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

AbstractThe complete1H and13C NMR assignments for 3,6‐epoxypentacyclo[6.2.2.02,7.04,10.05,9]dodecane and 3,6‐epoxypentacyclo[6.2.1.02,7.04,10.05,9]undecane are reported. The difference between the1H and13C chemical shifts and one‐bond proton‐carbon coupling constants of these two compounds are adequately explained by the difference in the hybridization of the C

ISSN:0030-4921    

DOI:10.1002/mrc.1270111010

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY

摘要:

AbstractNuclear screening tensors, their anisotropies and13C chemical shifts are calculated for a number of carbon environments and compared with the corresponding experimental data. The agreement found with the experimental results is an improvement over that obtained from CNDO/S parameterized calculations. The improvement stems from the inclusion of the one‐centre exchange integrals, which results in smaller values for the excitation energies from the INDO/S calculations. It is demonstrated that a linear relationship between13C chemical shift and the lowest energy transition is not to be expected. The average values of the excitation energies of the various transitions contributing to the13C screening are found to have significant variation

ISSN:0030-4921    

DOI:10.1002/mrc.1270111011

出版商:John Wiley&Sons Limited    

年代:1978

数据来源: WILEY