Magnetic Resonance in Chemistry

Brycki, Bogumil; Brzeziński, Bogumil; Grech, Eugeniusz; Malarski, Zbigniew; Sobczyk, Lucjan

doi: 10.1002/mrc.1260290603pmid: N/A

1H and 13C NMR spectra were studied for a number of 1,8‐bis(dimethylamino)naphthalene (DMAN) salts in acetonitrile‐d3. In the case of strong acids no counter anion effect was observed on the protonated DMAN molecules. A splitting of the 1H signal of the CH3 groups was found which was caused by coupling with the bridge NHN+ proton. It was confirmed that the salt with pentachlorophenol (PCP) undergoes a transformation to a nearly equimolar solution of free DMAN, protonated DMAN and the homoconjugated anion of PCP. The formation of the NHN+ bridge with an equally shared proton between the two nitrogen atoms leads to a change in the charge distribution in the naphthalene ring which is analogous to, but much weaker than, that found on protonation of aniline.

Podkorytov, I. S.; Lubnin, A. V.

doi: 10.1002/mrc.1260290604pmid: N/A

The 13C NMR spectra of models for the initial and terminal monomeric unit diads of polybutadiene are interpreted. The models are C10H18, diolefins, separated from the mixture of oligomers which are formed in the reaction of buta‐1,3‐diene with ethyllithium and a proton donor. A version of the INADEQUATE pulse sequence with DEPT polarization transfer and a selective DANTE read pulse is described and used for assignment.

Kitagawa, Susumu; Munakata, Megumu; Deguchi, Kenzou; Fujito, Teruaki

doi: 10.1002/mrc.1260290605pmid: N/A

Natural abundance 15N CP‐MAS NMR spectra of copper(I) complexes and their ligands, [Cu(biL)2]PF6 [biL = 1,10‐phenanthroline (phen) and 2,9‐dimethyl‐1,10‐phenanthroline (2,9‐Me2phen)], were measured. Coordination shifts of −45 and −44 (average) ppm were obtained for phen and 2,9‐Me2phen, respectively, which are attributed to the stabilization of the nitrogen lone‐pair orbital and the involvement of the metal d‐orbital via π‐back‐bonding.

Biekofsky, Rodolfo R.; Buschi, Carlos A.; Pomilio, Alicia B.

doi: 10.1002/mrc.1260290606pmid: N/A

13C NMR spectra of six flavones from Gomphrena martiana were analysed and compared with those of two related flavones isolated from Popowia cauliflora. This series of compounds has a similar substitution pattern on ring A, all compounds having oxygenated substituents on C‐5, C‐6 and C‐7. Consistent trends in relating conformation to substituent chemical shift effects (SCS) were found by analysing the 13C NMR data for these compounds. Chemical shifts for ring A carbons were calculated using the principle of additivity of substituents and by taking into account the conformation of the substituents. A reasonable agreement between the calculated shifts and the experimental values was found. A molecular mechanics study of these compounds was undertaken in order to obtain a set of consistent molecular structures to search for correlations between molecular structure and measured 13C chemical shifts. Good agreement was found between the predicted molecular mechanics conformations and the 13C NMR spectral data.

Béguin, Claude G.; Bennouna, Chakib; Bitar, Hassane; Dahbi, Abderrahman; Léna, Louis

doi: 10.1002/mrc.1260290607pmid: N/A

The characterization and determination of the protonated heteroatom content of the XH type (X = O, N, S) in oil fractions was carried out using 29Si NMR on silylated derivatives of the heteroatomic compounds. The analysis was achieved on a mixture of standard compounds and on two oil fractions from Morocco oil‐shale: asphaltenes and the aromatic and polar components.

Zieger, G.; Andreae, F.; Sterk, H.

doi: 10.1002/mrc.1260290608pmid: N/A

The assignment of proton NMR signals and the conformational analysis of N‐(Gly)–[Lys8]–vasopressin and N‐(GlyGlyGly)[Lys8]‐vasopressin in dimethyl sulfoxide solution by means of one‐ and two‐dimensional NMR techniques are presented. Dihedral angles obtained from 3J (HNCα‐H) vicinal couplings, intramolecular distances estimated from nuclear Overhauser enhancements (NOEs) and two‐dimensional experiments in the rotating frame (ROESY), as well as temperature dependences of the amide protons, suggest a more or less rigid ring conformation with an inverse γ‐turn for both cyclic peptides.

Alonso, Miguel E.; Pekerar, Sarah V.

doi: 10.1002/mrc.1260290609pmid: N/A

The electronic interaction between donor and withdrawing substituents on vicinal carbons of cyclopropane, leading to the possible participation of the cyclopropane ring in the mesomeric transmission, was examined in the terms of the variable electron density release of the donor group consequential to the variable electron density demand by the withdrawer. Based on the large anisotropic effect caused by the donor on the 1e" and 4e′ orbitals of cyclopropane that surround the corresponding geminal cyclopropyl proton, the 1H NMR spectra of 26 2‐(donor)‐1‐(acceptor) three‐membered carbocyclic derivatives were analysed for differential effects of C‐1 substituents, with variable electron‐withdrawing capacity, on their cis protons located on C‐2 and C‐3. It was found that 2‐aryloxy groups exert a strong modulation effect on δH‐2, making this proton notably less sensitive than H‐3 to changes in anisotropy modifications caused by the C‐1 group. 2‐Aryl groups, in contrast, affect proton resonances only to a limited extent. This was interpreted as an increased electron release on the 1e" and 4e′ LUMOs of cyclopropane by the C‐2 donor as electron demand increases in the C‐1 environment, and not as a consequence of conjugation through the ring.

Casu, Mariano; Anderson, Graeme J.; Choi, Gregory; Gibbons, William A.

doi: 10.1002/mrc.1260290610pmid: N/A

A combination of established lipid extraction procedures and high‐resolution 1D and 2D NMR spectroscopic methods has been used to analyse qualitatively and quantitatively the lipid composition of rat liver. The major lipids present in each structural class were identified and quantified. Considerable information on the composition of the different classes of structural and unsaturated fatty acid chains were obtained for the intact lipids without resort to hydrolysis. Significantly, the relative amounts of cholesterol, glycerophospholipids, ether lipids, sphingolipids and glycerides were shown to be in agreement with previous determinations by high‐performance liquid and other chromatographic procedures.