Magnetic Resonance in Chemistry

Delpuech, Jean‐Jacques

doi: 10.1002/mrc.1270020203pmid: N/A

L'inversion de l'azote pyramidal d'une amine peut ětre ralentie, de manière calculable, par une protonation presque totale dans un milieu d'acidité variable. Un traitement théorique complet permet de calculer sa vitesse à partir de la durée de vie moyenne du sel d'ammonium déterminée par résonance magnétique nucléaire. On peut ainsi fixer les conditions de validité de la formule approchée de Saunders et Yamada: la vitesse de protonation de l'amine doit ětre largement supérieure à la vitesse d'inversion; la vitesse de déprotonation du sel d'ammonium peut, par contre, ětre quelconque. Au cas où l'in version se produit entre deux molécules isomères différentes, ce traitement fournit également le rapport, à l'équilibre, des concentrations des sels isomères correspondants.

Lippmaa, E.; Pehk, T.; Andersson, K.; Rappe, C.

doi: 10.1002/mrc.1270020204pmid: N/A

Carbon‐13 spectra of 59 α,β‐unsaturated carboxylic acids have been measured. Large differential shieldings of ethylenic carbons in the cis and trans isomers of acrylic acid derivatives were found (altogether 15 isomeric Z‐ and E‐pairs of acids were investigated). The origin of differential shieldings is complex and both molecular ground states as well as changes in excited states appear to be involved. All measured 13C chemical shifts can be described by additive parameters that provide a straightforward new technique by which structural assignments can be made for a wide variety of isomeric mono‐, di‐ and tri‐ substituted α,β‐unsaturated acids.

Armarego, W. L. F.; Kobayashi, Toshihiko

doi: 10.1002/mrc.1270020205pmid: N/A

The PMR spectrum of trisformamidomethane in dimethyl sulphoxide‐d6 and hexamethyl‐phosphortriamide has been explained by postulating four major structures in solution: two rotamers and two structural isomers, all of which are stabilized by intramolecular hydrogen bonding to form six membered rings. The spectrum in trifluoroacetic acid is also described.

Conti, F.; Pietronero, C.; Viglino, P.

doi: 10.1002/mrc.1270020206pmid: N/A

Dipeptides of different amino acids have been studied by NMR in aqueous solutions at different pH values. The results obtained are discussed in terms of the different contributions to the chemical shift of the α‐CH protons.

Marty, Raymond; Houalla, Doureid; Wolf, Robert; Riess, Jean

doi: 10.1002/mrc.1270020207pmid: N/A

Dans les phosphinates d'alcoyle RPH(O)OR′, la présence de l'atome de phosphore asymétrique induit des inéquivalences magnétiques au niveau de protons ou groupes méthyles géminés. Si le reste alcoxy OR' comporte lui aussi un atome de carbone asymétrique, la résonance magnétique de 31P et de 1H, permet de mettre en évidence la formation des deux diastéréoisoméres attendus, en proportions égales.

Taddei, F.; Spagnolo, P.; Tiecco, M.

doi: 10.1002/mrc.1270020208pmid: N/A

PMR spectral parameters are reported for the isomeric trithienyl carbonium ions. The low field shifts, relative to the corresponding carbinols, are discussed in relation to the delocalization of the positive charge into the thiophene ring bonded in position 2 or 3. A linear correlation is found between chemical shifts and π‐charge densities and the proportionality constant is higher than that previously found for benzene derivatives. Vicinal coupling constants in these systems are satisfactorily in agreement with the corresponding calculated π‐bond order.

Kawasaki, Yoshikane

doi: 10.1002/mrc.1270020209pmid: N/A

Proton magnetic resonance spectra of a series of alkyl(oxinato)tin(IV) complexes, alkyl(oxinato)thallium(III), dimethylbis(oxinato)lead(IV), 8‐methoxyquinoline, 2‐methyl‐8‐hydroxyquinoline and 8‐hydroxyquinoline were studied. The indirect spin‐spin coupling constants J23, J34 and J24 of the oxinato ligand in the alkyl(oxinato)tin(IV) complexes and of 8‐methoxyquinoline were found to be 4.4 ± 0.2, 8.3 ± 0.2 and 1.7 ± 0.2 Hz, respectively. When the interaction between tin and nitrogen in the oxinato ligand is not strong as in trialkyl(oxinato)tin(IV), the resonance of the 2‐proton of the ligand shifts to high magnetic field relative to that of 8‐methoxyquinoline, but in the case of the strong interaction, as in dimethyl(oxinato)halogenotin(IV), the resonance is shifted to low magnetic field. The 4‐proton signals, however, shift monotonously to low magnetic field with increasing interaction. The behaviour of the 2‐proton signals was explained by a paramagnetic anisotropic effect of a nitrogen lone pair of the oxinato ligand and an intramolecular electric field effect and that of the 4‐proton by the latter effect. By comparing the change of the δ‐values of the 2‐, 3‐ and 4‐protons of the alkyl(oxinato)tin(IV) complexes and those of 8‐hydroxyquinoline by altering the solvents, from methylene chloride to benzene, it was found that the electron density around the 2‐carbon is reduced in the complexes compared with that of 8‐hydroxyquinoline.

Abraham, R. J.; Gatti, G.

doi: 10.1002/mrc.1270020210pmid: N/A

The 1H magnetic resonance spectrum of the title compound has been completely analysed, using 60, 100 and 220 MHz spectrometers. The values of the chemical shifts and coupling constants obtained confirm the proposed structure and also provide information on the conformation. The molecule is slightly boat‐shaped.