摘要:

AbstractCarbon‐13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H‐azirines. The higher field resonance of C‐2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C‐3 is indicated by a largeJ(13C‐3,H) value (

ISSN:0030-4921    

DOI:10.1002/mrc.1270091002

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractLa formation réversible d'un composé, résultant de l'addition de l'hexafluoroacétone sur les acides carboxyliques, a été mise en évidence par RMN1H,19F et infrarouge. Ce composé,, est le résultat d'une addition nucléophile de l'acide sur le carbonyle de l'hexafluoroacétone. Cette addition est favorisée par un abaissement de la température et la présence de substituants R donneurs d'électrons.D'autre part, le déplacement chimique des groupes CF3(ou du groupe OH) de ce composé dépend de la nature du substituant R, il est possible d'en déduire une méthode d'analyse

ISSN:0030-4921    

DOI:10.1002/mrc.1270091003

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

Abstract13C N.m.r. spectra have been determined for strychnine and a series of fourteen derivatives. The assignments are based on previously established data and on off‐resonance decoupled spectra. The shifts resulting from the alterations in molecular structure are discussed and explained, in part, as a consequence of conformational changes. This detailed study indicates that changes are required in some previously published assignment

ISSN:0030-4921    

DOI:10.1002/mrc.1270091004

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractLes effets de substituant des groupes méthyle et amino sur les déplacements chimiques de la pyrimidine ont été étudiés par RMN du proton et du carbone‐13 et comparés à ceux observés pour le benzène et la pyridine. Compte‐tenu des interactions mutuelles des substituants, les déplacements chimiques calculés à l'aide d'un schéma d'additivité sont en très bon accord avec les déplacements chimiques observés, sauf dans quelques cas concernant des pyrimidines encombrées. Cette étude des effets de substituant a permis l'attribution sans équivoque des spectres du carbone‐13 de

ISSN:0030-4921    

DOI:10.1002/mrc.1270091005

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractCorrection of measured chemical shifts by subtracting the diamagnetic contributions caused by certain substituents on various carbons of a molecule leads to data that allow a reasonable interpretation of substituent effects on chemical shifts in13C n.m.r. spectroscopy. It is shown that both paramagnetic and diamagnetic terms increase on all carbons of a molecule when the atomic number of a substituent increases down the same group of the periodic table. An explanation of α‐, β‐, and γ‐ effects for methyl substitution using the same procedure is a

ISSN:0030-4921    

DOI:10.1002/mrc.1270091006

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe addition of Co2+to D2O solutions of Nicotinamide Adenine Dinucleotide induces modifications of the13C n.m.r. signal line widths of these coenzymes. Analysis of the observed paramagnetic effects shows that both states (reduced and oxidized) and both conformations (folded or unfolded) of these coenzymes always allow two types of interactions between the cobalt ion and the nucleotide, namely where Co2+is linked to the phosphate groups and to nitrogen‐7 of the adenine nucleus. Moreover, the metal ion also interacts with the adenine NH2in the NAD+folded conformation. These natural abundance13C n.m.r. experiments allowed a fairly precise description of the Nicotinamide Adenine Dinucleotide—Co2+interacti

ISSN:0030-4921    

DOI:10.1002/mrc.1270091007

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe carbon–fluorine coupling constants in 33 different substituted benzotrifluorides (trifluoromethyl‐benzenes) have been determined. The3J(CF) to theorthoaromatic ring carbons varied between 1.7 and 5.6 Hz and, in a given molecule, were always larger than the5J(CF) to theparacarbon, which ranged between 0.7 and 1.7 Hz. Coupling to themetacarbons,4J(CF), was not observed and is under 0.3

ISSN:0030-4921    

DOI:10.1002/mrc.1270091008

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

Abstract13C N.m.r. chemical shifts obtained for indenyl‐ and cyclopentadienyllithium in several, mostly ethereal, solvents are presented. The chemical shift changes induced by varying the solvent are assumed to probe the actual π‐electron density distribution, thus providing an insight into the structure of the ion‐pair. The increase in the estimated π‐electron densities obtained for the protonated aromatic carbons of indenyllithium by increasing the coordinating ability of the solvent gives evidence of a change of the ion‐pair equilibrium towards solvent‐separated species. The average chemical shifts for indenyl‐ and cyclopentadienyllithium were independent of the choice of solvent, a fact which supports the ion‐pair model in

ISSN:0030-4921    

DOI:10.1002/mrc.1270091009

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

AbstractThe determination of structures and partial assignments of stereochemistry of juvabione and some of its analogues can be made on the basis of13C nuclear magnetic resonance studies. The complete13C n.m.r. spectral assignments for juvabione and five analogues are reported.

ISSN:0030-4921    

DOI:10.1002/mrc.1270091010

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY

摘要:

Abstract15N n.m.r. spectra of [13C‐2, 3‐15N2‐guanidino]arginine and [13C,15N2] urea were obtained in D2O and H2O at a variety of pH values both with and without proton decoupling. The effects of the proton exchange rate are readily observable in the proton coupled15N spectra. When theguanidinogroup is deprotonated (pK= 12.5), the terminal nitrogens give a single resonance 6.6 ppm downfield of the protonated species, indicating a rapid tautomeric exchange. The observed NH and CN couplings are compared with calculated values, and good agreement is found for1J(CN) using a Blizzard–Santry type calculation. The ramifications of the proton exchange on15N n.m.r. spectra of amino acids and peptides are di

ISSN:0030-4921    

DOI:10.1002/mrc.1270091011

出版商:John Wiley&Sons Limited    

年代:1977

数据来源: WILEY