Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260260701pmid: N/A

Doller, Darío; Gros, Eduardo G.

doi: 10.1002/mrc.1260260702pmid: N/A

The acid‐catalysed rearrangement of 3β, 16β‐dihydroxyandrost‐5‐en‐17‐one to 3β, 17β‐dihydroxyandrost‐5‐en‐16‐one was studied by 13C NMR spectroscopy. The spectra indicated that the reaction is produced by an intramolecular 1, 2‐shift of hydride from C‐16α to C‐17α.

Krishnamurthy, V. V.; Casida, John E.; Dohn, David R.

doi: 10.1002/mrc.1260260703pmid: N/A

Complete 13C and 1H spectral peak assignments of S‐(2,3‐dihydroxy‐1‐propyl)glutathione (1) (an in vivo metabolite of the pesticide 1,2‐dibromo‐3‐chloropropane) were made using various 2D NMR techniques. Long‐range CH correlation 2D NMR unambiguously assigned the key methylene resonances adjacent to sulfur. Appropriate delays for optimum cross‐peak intensities in the long‐range correlation experiment were chosen with response intensity curves, generated using estimated long‐range coupling constants. These curves, although generated assuming a first‐order coupling network, are useful even in systems with strong second‐order couplings as in 1.

Stegmann, Hartmut B.; Dao‐Ba, Hoang; Mäurer, Manfred; Scheffler, Klaus; Buchner, Hans; Hartmann, Erwin; Mannschreck, Albrecht

doi: 10.1002/mrc.1260260704pmid: N/A

A series of phenanthrenesemiquinone–diphenylthallium complexes were prepared in solution from the corresponding quinones. ESR, ENDOR and TRIPLE spectra provided the proton coupling constants and the unambiguous assignment to distinct molecular positions. The thallium splitting becomes considerably less negative if the semiquinones are twisted by steric hindrance in the 4‐ and 5‐positions. On the other hand, substitution in the 1‐ and 8‐positions renders aTI more negative. These results are interpreted in terms of steric hindrance of the ion‐pair solvation.

Morales‐Ríos, M. S.; Del Río, R. E.; Joseph‐Nathan, P.

doi: 10.1002/mrc.1260260705pmid: N/A

The 13C NMR spectra of all possible indoles substituted with one, two or three methyl groups on the pyrrole ring were assigned from heteronuclear two‐dimensional 13C/1H contour plots and homonuclear hydrogen‐hydrogen decoupling experiments at a specific concentration of 0.83 M in CDCl3 and in DMSO‐d6. The results confirm controversial assignments for some compounds, and provide the assignments for those compounds not previously studied by this technique. In addition, deuterium/hydrogen NMR isotope effect on 13C chemical shifts (DHIECS) for indoles, wherein the labile NH was partially exchanged to ND, are reported. In this way DHIECS values over two, three, four and five bonds were measured. The results in each solvent are discussed in terms of the number of bonds between the exchanged hydrogen and the observed carbon, and also according to their geometric dependence. This provides some evidence of the vibrational origin of the DHIECS.

Bigler, P.; Rychener, M.; Séquin, U.

doi: 10.1002/mrc.1260260706pmid: N/A

Heteronuclear NOEs have proved to be a valuable tool for the structure elucidation of an unexpected acylation product of dithranol. The application of a modified 2D HOESY pulse sequence with improved sensitivity is demonstrated.

Dimitrov, V. S.; Kurteva, V. B.; Lyapova, M. J.; Mikhova, B. P.; Pojarlieff, I. G.

doi: 10.1002/mrc.1260260707pmid: N/A

Unusually high free energies of activation for the rotation of phenyl groups, 12.1 and 11.1 kcal mol−1, are observed in the (1R*, 2S*, 3S*) and (1R*, 2R*, 3S*) isomers of 3‐(formylmethylamino)‐1,2,3‐triphenylpropyl chloride, and for the rotation of the formylmethylamino group (11.7 kcal mol−1) in the Z rotamer of the former isomer. These high barriers can be related to the interdependence of the rotation of such large planar groups in the strongly biased preferred conformations. The barriers for rotation of the formyl group are in the usual range (22.5 and 20.6 kcal mol−1) for (1R*, 2S*, 3S*) and (1R*, 2R*, 3S*) isomers, respectively.

Deutsch, W. Francis; Parkes, Harold G.; Shaw, Robert A.

doi: 10.1002/mrc.1260260708pmid: N/A

The temperature dependence of the 31P NMR spectra of N3P3Cl6, phenyl‐substituted cyclotriphosphazatrienes, N3P3PhnCl6‐n (n = 2, 4, 6), and a series of derivaties, N3P3Ph2(X(CH2)n Y)Cl2 (where X = Y = O, NH, n = 2, 3, 4; X = Y = NMe, n = 2, 3; X = NH, Y = NMe, n = 3), of gem‐N3P3Ph2Cl4 was studied. Differential changes in chemical shift as a function of temperature were observed between different 31P nuclei. In a number of cases second‐order effects could be greatly reduced through a change in temperature. The temperature dependence of the 31P shift was found to differ with solvent, for example when CDCl3 replaced CD2Cl2.

Liu, Zhong‐Li; Wu, Lung‐Min; Liu, You‐Cheng

doi: 10.1002/mrc.1260260709pmid: N/A

Benzoquinone cation radicals of 1,4‐benzoquinone and methyl‐, 2,5‐dimethyl‐ and 2,6‐dimethyl‐1,4‐benzoquinone were formed from the corresponding parent quinones by in situ UV photolysis in trifluoroacetic acid at ambient temperature, and detected by ESR. The cationic character of the radical species was confirmed by the electron transfer between the quinone cation radicals and N,N,Ń,Ń‐tetramethyl‐p‐phenylenediamine (TMPD). In the case of tert‐butyl substituted benzoquinones, instead of the corresponding cation radicals, cyclized radicals, i.e. the 3,3‐dimethylcoumaran‐5‐oxy and 3,3‐dimethyl‐7‐tert‐butylcoumaran‐5‐oxy radicals and the 3,3‐dimethyl‐6‐tert‐butylcoumaran‐5‐hydroxy cation radical were detected from tert‐butyl, 2,6‐di‐tert‐butyl‐ and 2,5‐di‐tert‐butyl‐1,4‐benzoquinones, respectively. A mechanism involving electron transfer between the photoexcited quinone and that in the ground state is proposed.

Tori, Motoo; Matsuda, Reiko; Sono, Masakazu; Asakawa, Yoshinori

doi: 10.1002/mrc.1260260710pmid: N/A

The 13C NMR chemical shifts of some dammarane‐type triterpenes, produced by oxidation of dammaran‐20(S)‐ol and 20(S)‐hydroxydammaran‐3β‐yl acetate with m‐chloroperbenzoic acid, were assigned by complete analysis of these compounds using 2D long‐range 13C1H correlation spectra and 2D INADEQUATE; it was found necessary to revise previous assignments. The 13C NMR signals of dendropanoxide were also analysed by 2D techniques including HHC relayed 13C1H correlation spectra.