ISSN:0030-4921    

DOI:10.1002/mrc.1270080912

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

Abstract13C chemical shifts for 23para‐ andmeta‐substituted chalcones of the types1and2have been determined. The aromatic shieldings are compared with previous results for other aromatic derivatives. Correlations of the13C chemical shifts of vinyl carbons and carbonyl carbons as well as ring carbons with Hammett σ parameters, π electron densities and the reactivity parameters of Swain and Lupton provide a consistent picture of electronic effects transmitted through the carbon framework of the compounds st

ISSN:0030-4921    

DOI:10.1002/mrc.1270080902

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractL'analyse des spectres RMN1H et13C d'une série de benchrotrènes mono‐et disubstitués a permis de discuter l'influence des substituants et spécialement les diastéréotopies associées à plusieurs types de chiralité. La forme racémique (pseudosymétrique) et les deux formesmeso(pseudoasymétriques) des glycols (OC)3CrC6H4(CHOHCH3)2sont comparées. Les implications stéréochimiques des résulta

ISSN:0030-4921    

DOI:10.1002/mrc.1270080903

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractThe influence of incorporating an group, an oxygen atom and the fragment in a saturated 7‐membered ring system on carbon‐13 n.m.r. chemical shifts is examined, and also, the influence of the dioxolane ring moiety on the13C chemical shifts in these ring systems. Substituent effects are generally additive except in cases where the ring is heavily substituted with methyl groups. A large upfield steric shift (γ effect) of 7–8 ppm is observed in two of the derivatives. An example of long range nonequivalence is also observed. Assignments of the13C n.m.r. spectra have been made by comparison with model compounds, and from proton coupled13C n.m.r. spectra. The synthesis of several new compounds is des

ISSN:0030-4921    

DOI:10.1002/mrc.1270080904

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractL'effet des groupements alkyle de la série Me, Et,i‐Pr,t‐Bu sur le déplacement des hydrogènes d'un groupe méthyle, situé enortho, est relié linéairement aux paramètres d'effets stériques (Es) de Taft dans des structures du type1.Une équation Δδ = δR– δMe= λ′Esrend compte des résultats expérimentaux. λ′ dépend du solvant et du modèle utilisé. Les calculs des déplacements chimiques suivant les approches d'ApSimon et de Buckingham confirment la prépondérance des effets stériques

ISSN:0030-4921    

DOI:10.1002/mrc.1270080905

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

Abstract13C n.m.r. spectra are reported for 1,3‐indandione, phthalic anhydride, thiophthalic anhydride, and phthalimide in chloroform‐dsolution. The13C chemical shifts have also been calculated by means of Pople's perturbation theory using CNDO/S wave functions; the agreement between theoretical and experimental values is improved when an empirical charge‐dependent term is added to the calculated diamagnetic and paramagneitc contribu

ISSN:0030-4921    

DOI:10.1002/mrc.1270080906

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractLes déplacements chimiques induits par Eu(fod)3sur plusieurs séries de sulfites cycliques à six chaînons permettent de déterminer les paramètresKcet ΔSRde l'équilibre de complexation pour une stoechiométrie supposée 1:1. La constante d'équilibre apparenteKcdécroît lorsque la substitution en 4 et 6 et la polarité du substituant en 5 augmentent en relation avec une augmentation de la fréquence d'élongationvSO en infrarouge. Ainsi, le groupe SO ax s'associera plus fortement que SO éq. Lorsqu'un équilibre conformationnel existe en l'absence de réactif lanthanidique, on peut prévoir qu'il évoluera avec lui vers une forme à SO ax. L'exploitation des ΔSRà l'aide de l'équation de pseudocontact confirme ces prévisions: (i) les formes chaises à SO ax sont stabilisées; (ii) les chaises à SO éq avec deux substituants éq en 4 et 6 présentent un équilibre avec quelques pourcents de conformation flexible à SO ax, surtout en l'absence de substituant ax en 5; (iii) les formes croisées d'axe 2–5 à SO intermédiaire ett‐Butransen 4 et 6 évoluent vers un bateau à O en proue et SO ax; (iv) let‐Bu‐5 oxo‐2 dioxathianne‐1,3,2trans, chaise àt‐Bu et SO axiaux pour ⋍70%, a son équilibre conformationnel complètement déplacé vers cette forme; (v) le triméthyl‐4,4,6 oxo‐2 dioxathianne‐1,3,2,cis, équilibre où interviennent les trois types de SO, s'associe essentiellement en conformation croisée d'axe 1–4 et à groupe SO ax. La plupart d

ISSN:0030-4921    

DOI:10.1002/mrc.1270080907

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

Abstract13C n.m.r. spectra of methyl substituted thianes and thianium cations have been determined. The magnitude of the13C substituent effects of an equatorial methyl group or of agem‐dimethyl grouping appear to depend in a systematic way on whether the carbon atom concerned is adjacent to, or removed from, the heteroatom. The shieldings are discussed in relation to the conformational properties of the thiane ring. Moreover, the average13C substituent parameters obtained from conformationally biased systems are applied to potentially mobile systems to assess the position of the conformational equilibriu

ISSN:0030-4921    

DOI:10.1002/mrc.1270080908

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

Abstract13C n.m.r. chemical shifts of a number of 1,1‐disubstituted ethylenes are presented. Moreover, effects of changing temperatures on the13C n.m.r. chemical shifts of some of these compounds as well as of three normal alkanes are given. These variations in chemical shifts are attributed to varying amounts of sterically induced shifts in the different conformational equilibria. In addition to the well‐known 1,4 interaction between two alkyl groups shielding effects on the carbon atoms of the connecting bonds are also proposed. No definite explanation of this effect is presented at this time. It is further shown that no simple correlations exist between13C n.m.r. chemical shifts and calculated total charge densities at this level. Instead, the experimental results in 1‐alkenes are rationalized by assuming a linear dependence of the13C n.m.r. chemical shifts of C‐1 and C‐2 via rehybridizations on changes in bond angles for small skeletal deformations caused by steric interactions. These changes in geometries, as well as conformational energies in three 1‐alkenes, were calculated by means of VFF calculations. Finally. upfield shifts for both C‐2 and C‐4 are proposed for those conformations of 1‐alkenes in which the C‐3C‐4 group interacts wi

ISSN:0030-4921    

DOI:10.1002/mrc.1270080909

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY

摘要:

AbstractIn the use of a shift reagent as an aid in the structural elucidation of organic compounds, it is shown that accurate measurements of the shift reagent and substrate concentrations are not needed to determine the relative bound shifts of the substrate and the chemical shifts of the free substrate spectrum with good precision. This is possible whenever the induced shift ratios of nuclei of a given molecule are independent of the shift reagent concentration. This independence has been verified for all the monofunctional compounds described in this paper. The effect of absolute substrate concentration, solvent, temperature and the presence of water on the relative bound shifts is studied using the eight methyl group signals of β‐amyrin. The method is demonstrated by its use for structural determinations in the ketoandrostane seri

ISSN:0030-4921    

DOI:10.1002/mrc.1270080910

出版商:John Wiley&Sons Limited    

年代:1976

数据来源: WILEY