Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270091001pmid: N/A

Isomura, Kazuaki; Taniguchi, Hiroshi; Mishima, Masaaki; Fujio, Mizue; Tsuno, Yuho

doi: 10.1002/mrc.1270091002pmid: N/A

Carbon‐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 large J(13C‐3,H) value (242.5 Hz).

Pellissier, N.

doi: 10.1002/mrc.1270091003pmid: N/A

La formation réversible d'un composé, résultant de l'addition de l'hexafluoroacétone sur les acides carboxyliques, a été mise en évidence par RMN 1H, 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.

Verpoorte, R.; Hylands, P. J.; Bisset, N. G.

doi: 10.1002/mrc.1270091004pmid: N/A

13C 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 assignments.

Riand, J.; Chenon, M. T.; Lumbroso‐Bader, N.

doi: 10.1002/mrc.1270091005pmid: N/A

Les 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 pyrimidines trisubstituées.

Shahab, Y. A.

doi: 10.1002/mrc.1270091006pmid: N/A

Correction 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 in 13C 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 attempted.

Torreilles, Jean; De Paulet, André Crastes; Platzer, Nicole

doi: 10.1002/mrc.1270091007pmid: N/A

The addition of Co2+ to D2O solutions of Nicotinamide Adenine Dinucleotide induces modifications of the 13C 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 NH2 in the NAD+ folded conformation. These natural abundance 13C n.m.r. experiments allowed a fairly precise description of the Nicotinamide Adenine Dinucleotide—Co2+ interactions.

Newmark, Richard A.; Hill, James R.

doi: 10.1002/mrc.1270091008pmid: N/A

The carbon–fluorine coupling constants in 33 different substituted benzotrifluorides (trifluoromethyl‐benzenes) have been determined. The 3J(CF) to the ortho aromatic ring carbons varied between 1.7 and 5.6 Hz and, in a given molecule, were always larger than the 5J(CF) to the para carbon, which ranged between 0.7 and 1.7 Hz. Coupling to the meta carbons, 4J(CF), was not observed and is under 0.3 Hz.

Edlund, Ulf

doi: 10.1002/mrc.1270091009pmid: N/A

13C 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 all studied media.

Manville, John Fieve; Bock, Klaus

doi: 10.1002/mrc.1270091010pmid: N/A

The determination of structures and partial assignments of stereochemistry of juvabione and some of its analogues can be made on the basis of 13C nuclear magnetic resonance studies. The complete 13C n.m.r. spectral assignments for juvabione and five analogues are reported.