Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270130501pmid: N/A

Besserre, D.; Coffi‐Nketsia, S.

doi: 10.1002/mrc.1270130502pmid: N/A

The conformation of some 2‐σ‐1,3,2‐dioxaphospholanes (σ=OAlkyl, CI) is studied. The determination of the 2J(POC) and 3J(POCC) coupling constants, which are influenced by the bulk of the alkoxy group, is a means of obtaining information about the rotation around the POR bond, which is dependent on steric interactions between the phosphorus lone pair, the alkoxy group and the substituents on the ring. When σ is a tert‐butoxy group, a direct ‘through‐space’ interaction is found between the phosphorus atom and one of the primary carbons of the OR group. If there is no substituent on the ring, the 31P chemical shifts are little affected by changes in OR; a diamagnetic effect is observed, however, in the case of the tert‐butoxy group which is enhanced for the 4,4,5,5‐tetramethyl derivatives.

Laitem, Leopold; Christiaens, Leon; Renson, Marcel

doi: 10.1002/mrc.1270130503pmid: N/A

An important 13C NMR shielding effect on carbons bearing a heavy chalcogen is demonstrated. This effect is parallel to that induced by iodine, but to a lesser extent. For acyclic compounds and for partially saturated heterocycles, there is an excellent linear correlation between the 13C chemical shifts of carbons bearing a chalcogen and carbons bearing a halogen atom in the corresponding compound. The linearity of the relationship is less satisfactory with heteroaromatic compounds.

Rouillard, Michel; Geribaldi, Serge; Khazarian, Jean; Azzaro, Marcel

doi: 10.1002/mrc.1270130504pmid: N/A

The changes in chemical shift induced by isomerization for all the ring protons of the Z‐ and E‐5,5‐dimethyl‐2‐cyclohexenylidene acetonitriles depend only on the through‐space effects of the cyano group. The configurational assignments were made taking into consideration the anisotropic and electric field effects, either separately or together. In the first case, the total effects are ΔXCNT=−14.7×10−6cm3 mol−1 and bμCNT=14.7×10−30 cm3, respectively. The second approach allows the estimation of the values ΔXCN=−4.9 × 10−6 cm3 mol−1 and bμCN=9.8 × 10−3 cm3, reflecting the combined contributions of magnetic anisotropy and electric field to the total effect.

Arcelli, Antonio; Bongini, Alessandro; Budini, Rolando

doi: 10.1002/mrc.1270130505pmid: N/A

The composition of the mixture from the reaction of the basic amino acids ornithine or lysine with pyridoxal‐5′‐phosphate was investigated in D2O by 1H NMR and was found to be dependent on pH, α attack being favoured at acid pH and ω attack in basic solutions.

Daunis, Jacques; Follet, Michel; Marzin, Claude

doi: 10.1002/mrc.1270130506pmid: N/A

13C NMR spectroscopic data are reported for the s‐triazolo‐as‐triazinones of five isomeric series. Comparison of their 13C chemical shifts and CH coupling constants allows the determination of the type of ring junction of the two heterocycles, as well as the predominant tautomeric form in each system.

Kricheldorf, Hans R.; Hull, William E.

doi: 10.1002/mrc.1270130507pmid: N/A

The natural abundance 15N NMR spectra of glycylglycine and alanylalanine derivatives with various N‐ or O‐protecting groups were measured in dimethyl sulphoxide, pyridine and fornic acid. The nitrogens directly attached to the protecting group have chemical shifts relative to NO3− in the range −220 to −358 ppm. The influence of the amino end group on the next peptide nitrogen (Gly‐Gly bond) amounts to, at most, 1.7 ppm. The influence of the O‐protecting group is also weak (Δ δ⩽2 ppm), but strongly dependent on the solvent.

Fruchier, Alain; Elguero, José; Hegarty, Anthony F.; McCarthy, Daniel G.

doi: 10.1002/mrc.1270130508pmid: N/A

Assignment of the carbon resonances in nine derivatives of N‐hydroxybenzotriazole has been carried out. The 13C NMR method enables tautomeric N‐hydroxy and N‐oxide and isomeric O‐ and N‐acyl structures to be identified. In DMSO, the predominant tautomer of N‐hydroxybenzotriazole was found to be the N‐hydroxy form. The structure of the benzoate and methyl and phenyl carbonate esters were likewise established, but for the two latter compounds, hydrolysis of the equilibrating O‐ and N‐acyl isomers imposed some limitations on the usefulness of the technique.

Wasylishen, Roderick E.; Friesen, Kenneth J.

doi: 10.1002/mrc.1270130509pmid: N/A

Carbon‐13 NMR spectra of solid polycrystalline bicyclo[3.3.1]nonan‐9‐one and adamantanone have been measured at 315K. The relatively narrow 13C linewidths observed for these solids, together with measured spin‐lattice relaxation times, indicate that both these solids are orientationally disordered. Observed 13C chemical shifts of solid bicyclo[3.3.1]nonan‐9‐one indicate a twin‐chair conformation for the two cyclohexanone rings.

Banerji, A.; Siddhanta, A. K.; Acharyya, A. K.; Dutta, C. P.

doi: 10.1002/mrc.1270130510pmid: N/A

13C NMR spectra of six kawa‐pyrones (styryl α‐pyrones) have been assigned. The assignments are based on the splitting pattern in the coupled spectra, comparison of the chemical shifts with those of model compounds and by application of additivity relationships. The 13C NMR of styrene was also reinvestigated.