Magnetic Resonance in Chemistry

Roques, B. P.; Prange, T.; Oberlin, R.

doi: 10.1002/mrc.1270090403pmid: N/A

L'étude des interactions solvant/soluté des quatre benzothiénopyridines isomères a été entreprise par RMN 1H. Le calcul des spectres au second ordre permet de révèler: (i) dans l'acétone une orientation préférentielle des molécules de solvant au niveau du cycle pyridinique; (ii) une forte variation des couplages de la partie benzénique en fonction de la nature du solvant; (iii) une interaction préférentielle du cycle pyridinique dans les complexes de collision du benzène. Ces résultats peuvent ětre transposés aux interactions hétérocycles azotés/bases appariées de l'ADN (intercalation).

Mazurek, M.; Mallard, T. M.; Gorin, P. A. J.

doi: 10.1002/mrc.1270090404pmid: N/A

13C FT n.m.r. spectra were obtained from borates of methyl α‐D‐glucopyranoside, triethylboron, sodium tetraphenylboron and 1‐butaneboronic acid employing a simultaneous 1H and 11B decoupling network. The effectiveness of the system was evident using the three latter organoboron compounds. Since no diminution in line broadening of signals occurred in the spectrum of the sugar borate, the absence of 13CO11B coupling was indicated. This finding was confirmed by comparing the effects of varying the temperatures of sugar borates and triethylboron on their conventional 13C n.m.r. spectra.

Edlund, Ulf; Norström, Åke

doi: 10.1002/mrc.1270090405pmid: N/A

Carbon‐13 n.m.r. chemical shifts are reported for diphenyl ether and several of its chlorinated analogs. Carbon shieldings were found to be dependent on the degree of steric interference to conjugative release by the oxygen atom. Substituent effects due to attached chlorine atoms seem to be more easily transmitted into the adjacent aryl moiety if the number of ortho chlorines is reduced. These results were clearly seen by a variable‐by‐variable plot display or by using a pattern recognition computer program. Spin‐lattice relaxation times have been measured for several compounds mainly for assignment purposes, but they are also briefly discussed in view of possible interconversion mechanisms.

Nishida, Toshiaki; Wahlberg, Inger; Enzell, Curt R.

doi: 10.1002/mrc.1270090406pmid: N/A

13C n.m.r. studies of a series of tricarbocyclic ring C aromatic diterpenoids using proton‐noise and single‐frequency off‐resonance decoupling, partially relaxed Fourier transform techniques, shift reagents and specifically labelled derivatives have permitted unequivocal assignments of almost all signals. The shieldings caused by oxygenation of C‐18 and C‐19 and by introduction of various substituents in the aromatic ring are discussed. It is concluded that the 13C n.m.r. data are sufficiently characteristic to allow stereochemical assignments. Some effects of deuterium substitution on the carbon resonances are presented.

Batts, B. D.; Pasaribu, S. J.; Williams, L. R.

doi: 10.1002/mrc.1270090407pmid: N/A

An accurate measurement of the chemical shifts and the coupling constants of some disubstituted acetophenones has been made. The acetophenones studied contained nitro, bromo or amino groups substituted in either the 3,4 or 2,5 positions. For compounds with no substituent adjacent to the acetyl group, the chemical shifts and the coupling constants estimated by the simple additivity of the substituent increments were found to be in reasonable agreement with the experimental values. The two nitro, bromo derivatives substituted in positions 2 and 5 probably prefer the conformer in which the proton H‐6 is adjacent to the acetyl methyl group whilst the 3,4‐disubstituted bromo, nitro and bromo, amino derivatives prefer the conformer in which the H‐6 proton is adjacent to the carbonyl group.

Gronowitz, S.; Konar, A.; Hörnfeldt, A.‐B.

doi: 10.1002/mrc.1270090408pmid: N/A

77Se N.m.r. spectra of 4,4′‐disubstituted diphenyl selenides have been obtained. The chemical shifts could be correlated with substituent constants of the Hammett type or with Swain and Lupton two‐parameter equations. No correlations were observed between these 77Se shifts and the 13C shifts of the CH2 group of 4,4′‐disubstituted diphenylmethanes, the latter shifts showing no correlation with substituent constants. On the other hand linear correlation was observed between the 77Se shifts of the 4,4′‐disubstituted diphenyl selenides and the 1H shifts of the CH2 group of the diphenylmethanes, the 13C shifts of their 1‐carbons and the 19F shifts of 4‐substituted fluorobenzenes.

Zetta, L.; Gatti, G.

doi: 10.1002/mrc.1270090409pmid: N/A

The conformations of dihydrolysergamides and 10‐methoxydihydrolysergamides have been inferred from the study of the chemical shifts of the amide hydrogens and their temperature dependence. The 13C chemical shifts have been shown to be sensitive to conformational changes of the piperidine ring. The results indicate that the conformation of the latter depends both on the substituent in position 10 and on the solvent.

Manatt, Stanley L.

doi: 10.1002/mrc.1270090410pmid: N/A

It has been found that LAOCOON III can fail to converge for some strongly coupled AA′BB′ spin systems unless trial coupling constants and chemical shifts within a few tenths of a Hz of the real parameters are used to initiate the iteration. This problem seemed linked to those spin systems possessing two or more pairs of energy levels which are nearly degenerate. In the cases where LAOCOON III failed, the program NMRENIT always yielded the correct, converged, iterative solution even with completely arbitrary starting parameters. The latter program also appears to accomplish a given number of iterations with an AA′BB′ system roughly three times as fast as the former program.