Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270111101pmid: N/A

Lewis, P. M. E.

doi: 10.1002/mrc.1270111114pmid: N/A

Dalrymple, D. L.; Wilkins, C. L.; Milne, G. W. A.; Heller, S. R.

doi: 10.1002/mrc.1270111102pmid: N/A

A data base containing approximately 4000 13C nuclear magnetic resonance spectra has been assembled. The spectra have been evaluated and all the corresponding compounds have been registered by the Chemical Abstracts Service (CAS). The data base is available to the international scientific community on magnetic tape or microfiche and is also the basis of a search system operating upon an international computer network.

Cox, Richard H.; McKinney, James D.

doi: 10.1002/mrc.1270111103pmid: N/A

Carbon‐13 NMR spectra have been obtained for aldrin, dieldrin, isodrin, endrin, heptachlor, heptachlor oxide and 24 of their degradation/conversion products. Chemical shifts were assigned on the basis of (1) comparison among the spectra, (2) single frequency, off‐resonance decoupling experiments, (3) substituent effects derived for norbornanes and (4) spectra obtained with an added lanthanide shift reagent. The substituent effects previously reported for norbornanes were found to be applicable for establishing trends in the chemical shifts for many of the compounds studied.

Davoust, Daniel; Massias, Marcel; Molho, Darius; Platzer, Nicole; Basselier, Jean‐Jacques

doi: 10.1002/mrc.1270111104pmid: N/A

L'interaction des sels de lanthanide avec des phénols en solution dans le DMSO a été étudiée en RMN en vue de la détermination de structure de polyphénols naturels. Par des expériences de compétition intermoléculaire, il a étée possible de mettre en évidence des différences de réactivité en fonction de la nature et de la position des substituants. Des règles empiriques de réactivité ont été proposées; elles ont permis d'interpréter les variations de déplacements chimiques observées dans le spectre de RMN de polyphénols naturels (flavones, xanthones) en présence de sel de lanthanide.

Äyräs, Pertti; Widén, Carl‐Johan

doi: 10.1002/mrc.1270111105pmid: N/A

Proton coupled 13C NMR spectra have been recorded for some acylphloroglucinol derivatives. Significant couplings over two, three and four bonds were observed between the hydroxyl proton and aromatic carbons for those compounds where the hydroxyl group is hydrogen bonded strongly enough to the carbonyl carbon of the acyl side chain. Typical values were 2J = 4.8 Hz, and 3J = 5.6 Hz or 6.7 Hz corresponding to dihedral angles of c. 0° and c. 180°, respectively; the dihedral angle is defined as the angle between the O—H bond and the plane of the aromatic ring. A stereospecific 4J(COH) value of 1.2 Hz for a ‘W’ arrangement of coupled atoms was also found. An interesting example of ‘virtual’ J(CH) coupling was observed in the proton coupled spectrum of 1‐butyrylphloroglucinol 2‐monomethyl ether in acetone‐d6 caused by the accidentally equal chemical shifts of the two ring protons.

Berg, Ulf; Sjöstrand, Ulf

doi: 10.1002/mrc.1270111106pmid: N/A

Complete 1H NMR bandshape analysis has been used to study the rotational barrier around the carbon–carbon double bond in two types of polarized ethylenes; on the one hand for planar ketene mercaptals (A), for which the hindered rotation over the 90 degrees twisted transition state is measured and, on the other hand, for sterically hindered ketene aminals (B and C) which are twisted in the ground state, and have measurable barriers over a planar, sterically crowded transition state. For compounds A activation entropies of the order of −45 to −76 J mol−1 K−1 (−11 to −8 cal mol−1 K−1), and for compounds B and C +28 to +42 J mol−1 K−1 (+7 to +10 cal mol−1 K−1) were obtained. This important difference was interpreted in terms of opposite charge development during the course of the rotation in the two cases, with concomitant reversed changes in the orientations of the solvent. The effects of solvent polarity and the presence of acid are shown to be reversed for the two types of compounds. A more polar solvent, and, in particular, addition of small amounts of acid decrease the barrier in system A but increase the barrier in systems B and C. A large negative entropy of activation was found for the acid‐catalyzed process, ΔS≠ = −107 J mol−1 K−1 (−25.5 cal mol−1 K−1). This low value is briefly discussed in relation to the mechanism of the acid‐catalyzed rotation.

Mann, G.; Kleinpeter, E.; Werner, H.

doi: 10.1002/mrc.1270111107pmid: N/A

Die 13C‐NMR‐Spektren einer Reihe von Cyclohexanen mit 1,3‐diaxialen Methylgruppen wurden bestimmt. Die Resonanzsignale der Methyl‐Kohlenstoffatome 1 und 3 sind in diesen Verbindungen um durchschnittlich 4,5 ppm nach tieferem Feld verschoben (δ‐Effekt). Auch die Ringkohlenstoffatome 1 und 3 zeigen Verschiebungen um durchschnittlich 0,7 ppm nach tieferem Feld (γ‐Effekt). In offenkettigen Kohlenwasser‐stoffen werden analoge Verschiebungseffekte beobachtet, wenn in den betreffenden Verbindungen die Geometrie des gPgM‐Konformeren des n‐Pentans vorkommt.

Su, Ja‐An; Siew, Ernest; Brown, Ellis V.; Smith, Stanford L.

doi: 10.1002/mrc.1270111108pmid: N/A

Carbon‐13 chemical shift assignments are reported for four chloroquinolines, six chloroisoquinolines, one dichloroquinoline, four dichloroisoquinolines, four methylchloroquinolines, two methylchloroisoquinolines, quinoline N‐oxide, isoquinoline N‐oxide, five methylquinoline N‐oxides, two methylisoquinoline N‐oxides and three chloroisoquinoline N‐oxides. Chlorine substituent chemical shift (SCS) effects are reported for the alpha, ortho, meta, para and peri positions. Consistent patterns are observed for the para and peri positions, a vinylogous ortho pattern is reported and the additivity of these SCS effects is demonstrated. Alpha SCS effects vary widely from 1.1 ppm upfield in 1‐chloroisoquinoline to 6.7 ppm downfield in 4‐chloroquinoline. These results, together with those in the literature, permit the definition of steric and nitrogen lone‐pair contributions which modify the ‘normal’ chlorine SCS effect, and these modifying contributions are shown to be roughly additive.

Iratçlabal, P.; Grenier‐Loustalot, M. F.; Lichanot, A.; Métras, F.

doi: 10.1002/mrc.1270111109pmid: N/A

L'étude RMN 13C et 1H à basse température des chloro‐4 et bromo‐4 méthylènecyclohexanes nous a permis de déterminer les paramètres d'activation associés aux équilibres conformationnels de ces composés. Les résultats obtenus montrent que d'un point de vue dynamique les substituants Cl et Br ont la měme influence en séries cyclohexanique et méthylènecyclohexanique.