Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270120501pmid: N/A

Gouesnard, J. P.; Martin, G. J.

doi: 10.1002/mrc.1270120502pmid: N/A

13C and 15N spectroscopies at natural abundance have been applied to the study of nitrogen lone‐pair delocalization in NN containing compounds: nitrosamines, nitramines, hydrazines, hydrazones and triazenes. Structure‐chemical shift correlations have been derived for nitrosamines; the 13C upfield effect of a γ substituent has been used for assigning the configuration of both diastereoisomers in N,N‐unsymmetrically substituted nitrosamines. Equations have been computed which permit the prediction of the electronic delocalization, expressed in terms of free enthalpy of activation ΔG ≠298, as a function of δ15N and of the length of the NN bond. 15N spectroscopy has also been applied to the study of the protonated species of nitrosamines and of acceptor‐donor complexes of nitrosamines with Lewis acids. The behaviour of such NN containing compounds is compared to that of amides.

Roth, Klaus

doi: 10.1002/mrc.1270120503pmid: N/A

Die Anwendung der ‘inversion‐recovery’ und ‘progressive saturation’ Techniken erlaubt unter geeigneten experimentellen Bedingungen die selecktive Unterdrückung von NMR‐Signalen. Mit Hilfe beider Techniken können verdeckte Signale nachgewiesen werden, wie am Beispiel des 13C Spektrums des Phthalsäurediäthylesters und dem 1H Spektrum des Indenylanions gezeigt wird.

Jallali‐Heravi, M.; Webb, G. A.; Witanowski, M.

doi: 10.1002/mrc.1270120504pmid: N/A

Some INDO/S parameterized calculations of local diamagnetic contributions to some carbon and nitrogen screening constants are reported. It is shown that Pople's local term model provides data which are in satisfactory agreement with X‐ray photoelectron results. The restricted atom‐dipole model also provides reasonable agreement. However the complete atom‐dipole expression is found to be incompatible with the experimental data due to the presence of a non‐local contribution.

Delaunay, Jacques; Lebouc, Alain; Riobé, Olivier

doi: 10.1002/mrc.1270120505pmid: N/A

L'étude RMN 1H des alkyl‐2 chloro‐3 tétrahydropyrannes, préparés par action des réactifs de Grignard sur le mélange des dichloro‐2,3 tétrahydropyrannes cis et trans, indique la présence de deux isomères cis et trans, dans lesquels les groupements alkyles sont en position équatoriale; le chloro‐3 phényl‐2 tétrahydropyranne n'existe que sous la forme trans (éq‐éq). L'étude RMN 1H des alcoxy (aryloxy)‐2 tétrahydropyranne n'existe que sous la forme trans (éq‐éq). L'étude RMN 1H des alcoxy (aryloy)‐2 chloro‐3 tétrahydropyrannes cis et trans, obtenus par action d'alcools et du phénol sur les měmes dérivés dichlorés, montre que le groupement alcoxyle (ou aryloxyle) est toujours en position axiale.

Diehl, P.; Bösiger, H.; Jokisaari, J.

doi: 10.1002/mrc.1270120506pmid: N/A

The indirect ortho and para carbon‐carbon coupling constants in benzene were determined utilizing the deuterium isotope effect on the carbon chemical shifts in 1‐d1‐ and 1,3,5‐d3‐benzene. The measurements gave for J(CC, ortho) and J(CC, para) the values of 55.3 ± 0.5 Hz and 10.08 ± 0.10 Hz, respectively. The ratios of the direct dipolar CC coupling constants were calculated using the previous results of 1‐13C‐benzene in an oriented phase. These ratios differ from the theoretical ones obtained assuming the benzene ring to be hexagonal, showing significant indirect contributions in the D values.

Rabaron, A.; Didry, J.‐R.; Kirkiacharian, B. S.; Plat, M. M.

doi: 10.1002/mrc.1270120507pmid: N/A

Les déplacements chimiques du 13C et les constantes de couplage 13C‐1H d'hydroxy‐4 coumarines et d'hydroxy‐4 méthoxy‐7 coumarines substituées en 3 sont déterminés. Une corrélation à 3 paramètres: ℱ et ℛ de Swain et Lupton et Q de Schaefer appliquée à ces deux séries établit les relations linéaires qui permettent de prévoir les déplacements chimiques à partir des paramètres des substituants.

Milne, G. W. A.; Zupan, J.; Heller, S. R.; Miller, J. A.

doi: 10.1002/mrc.1270120508pmid: N/A

A link between a substructure searching system and a 13C NMR data base has been established and permits the retrieval and examination of the chemical shifts associated with specific substructures. The means by which these searches are accomplished is described and the results from the searches are presented and discussed. The system is interactive, and can be used to locate in the data base the chemical shifts of carbon atoms in precisely defined environments. Alternatively, it may be used to learn the range of the chemical shifts possessed by particular types of carbon atoms, such as N‐methyl or O‐methyl carbons.

Burnell, E. E.; Marshall, A. G.; Roe, D. C.

doi: 10.1002/mrc.1270120509pmid: N/A

The proton NMR spectrum of 2‐fluoropyridine partially oriented in a nematic phase has been analyzed, and the geometry of the proton and fluorine skeleton and the order matrix have been determined. The structure does not differ significantly from that of pyridine in a nematic solvent, and the largest positive order parameter axis lies approximately along the CF bond direction in the molecule.

Anet, Frank A. L.; Easton, N. Roy; Yavari, Issa

doi: 10.1002/mrc.1270120510pmid: N/A

The natural‐abundance 13C NMR spectra of cis,cis‐1,5‐cyclooctadiene monoepoxide and cis,syn,cis‐1,5‐cyclooctadiene diepoxide have been investigated over the temperature range of – 10 to – 180°C. Whereas the spectra of the former showed no dynamic NMR effect, two different conformations in the ratio of 3:1 were observed at low temperatures for the latter. The free‐energy barrier (ΔG≠) for conversion of the major conformation to the minor conformation is calculated to be 5.9°0.2 kcal mol−1 from a line‐shape analysis of spectra obtained at intermediate temperatures. It is shown that cis,syn,cis‐1,5‐cyclooctadiene diepoxide exists in solution in chair (major) and in twist‐boat (minor) conformations of slightly different energies. Interconversion paths between these conformations are discussed. The monoepoxide is suggested to have a twist‐boat conformation that is rapidly pseudorotating via a boat conformation even at – 180°C.