Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270140601pmid: N/A

Benn, Reinhard; Schroth, Gerhard

doi: 10.1002/mrc.1270140602pmid: N/A

The 1H NMR spectra of various alkyl substituted η3‐allyl transition metal complexes (MNi, Ru) have been analysed. The chemical shifts of the η3‐allyl protons can be calculated using additive increments; the values of the syn and anti vicinal proton‐proton coupling constants approach each other on alkyl substitution of the η3‐allyl group.

Diaz, E.; Rojas‐Dávila, E.; Guzmán, A.; Joseph‐Nathan, P.

doi: 10.1002/mrc.1270140603pmid: N/A

The determination of the enantiomeric composition of 2,2′,6′6′‐tetrasubstituted biphenyls using 1H NMR spectroscopy, in combination with chiral lanthanide shift reagents, has been studied. In general, the S compounds give largeer induced shifts than the correspondind R isomers when d‐camphor derived shift reagents are used.

Frahm, August W.; Hambloch, Heinrich F.

doi: 10.1002/mrc.1270140604pmid: N/A

The 13C NMR chemical shifts of the C‐1′ carbon atom of fifteen para‐substituted benzophenones correlate with the ℱ and ℛ substituent constants in a reversed manner.

Hasan, Misbah Ul

doi: 10.1002/mrc.1270140605pmid: N/A

Carbon‐13 NMR chemical shifts in various amides and imides are examined. The compounds include mono‐ and diamides, acyclic imides and cyclic 5‐ and 6‐membered ring imides. The observed shifts can be satisfactorily rationalized on the basis of various electronic and steric factors which contribute to the chemical shifts in these systems. The 13C shifts in amides and imides are further compared with the shifts in corresponding oxygen analogues, i.e. esters and anhydrides. The saturated and α, β‐unsaturated amide carbonyls absorb in the range of 173–178 ppm and 167–170 ppm, respectively. These shifts are downfield by 2–3 ppm in comparison with the corresponding esters. The carbonyl shifts in cyclic imides appear in the range 170–180 ppm. In comparison with the corresponding anhydrides and amides, these shifts are downfield by 5–7 ppm and 3–4 ppm, respectively. These differences are discussed in terms of electronic interactions and steric effects.

Iratçabal, Pierre; Grenier‐Loustalot, Marie‐Florence; Lichanot, Albert; Metras, Franck

doi: 10.1002/mrc.1270140606pmid: N/A

A dynamic study of spirocyclohexanes was carried out using low‐temperature 13C nuclear magnetic resonance spectroscopy. The variations of the energy barrier to inversion of the cyclohexane ring are interpreted in terms of the electronegativity of the heteroatoms of the spiro substituent.

Kricheldorf, Hans R.

doi: 10.1002/mrc.1270140607pmid: N/A

The 15N13C coupling constants of 15N‐enriched acetamide, N‐acetylglycine anilide, phthalimide, α,α′‐bisphthalimido‐p‐xylene, N‐methyl‐N′‐phenylurea, poly‐L‐alanine and poly‐L‐valine were measured in various solvents. It was found that the 15N13C coupling constants depend largely on the nature of the solvent. Increasing acidity leads to higher one‐bond and lower two‐bond coupling constants. A change of concentration does not have any influence on the 15N13C couplings while a large increase in temperature leads to a slightly lower 1J(NC). It is concluded that solvent effects may limit the use of 15N13C coupling constants for the elucidation of solvent‐induced conformational changes.

Carpenter, Roshan C.; Sotheeswaran, Subramaniam; Sultanbawa, M. Uvais S.; Ternai, B.

doi: 10.1002/mrc.1270140608pmid: N/A

The 13C NMR spectra of eight triterpenes are recorded and all carbon shifts have been assigned. The data are in agreement with the structures assigned to the rare lupanediol, lup‐20(29)‐ene‐3α,23‐diol, and other lupane triterpenes isolated from the Sri Lankan Glochidion species (Euphorbiaceae). The 13C NMR data of some triterpenes, aleuritolic acid derivatives and taraxerane derivatives are compared.

Braun, S.; Kinkeldei, J.; Walther, L.

doi: 10.1002/mrc.1270140609pmid: N/A

In order to study the structure dependence of the 13C,H coupling constants in polycyclic conjugated π electron systems with 5‐and 7‐membered rings, the 1H coupled 13C NMR spectra of aceheptylene, azulene and 5‐azaazulene have been analysed. The results are discussed, including published data of monocyclic reference compounds, and are compared to theoretical values calculated by the FPT‐INDO method. It is shown that, first, the geminal 13C,H couplings in the unsaturated 5‐membered carbocycles are predominantly dependent on CC bond lengths. Second, the vicinal 13C,H coupling constants in 5‐ as well as in 7‐membered unsaturated carbocyclic rings can be linearly related to the lengths of the central CC bonds. Third, the vicinal inter‐ring couplings show a large variation and give information on ring junction, thus being of special value in structure determination and are governed mainly by the bond angles. Fourth, the calculated 13C,H couplings across one and two bonds are totally useless for practical purposes; those across three bonds, however, at least reflect the experimental trends.

Langford, Gordon E.; Yates, Peter; Yeung, Hin Wing; Cheng, Kin Fai

doi: 10.1002/mrc.1270140610pmid: N/A

The 13C NMR spectra of leonurine hydrochloride and thirteen of its analogues in DMSO‐d6 have been analyzed. Changes in the aromatic substituents have no significant effect on the chemical shifts of the side chain methylene carbons indicating that they do not influence the conformation of the latter. Observed deviations from additivity of substituent effects for the methylene carbon chemical shifts suggest that the methylene side chains of these compounds may be more tightly coiled than are the corresponding n‐alkanes. In representative cases no change in conformation is evident in 50% aqueous DMSO‐d6 solutions, indicating that similar considerations may apply in aqueous media.