Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270121001pmid: N/A

Browne, C. E.; Ruehle, P. H.; Dobbs, T. K.; Eisenbraun, E. J.

doi: 10.1002/mrc.1270121002pmid: N/A

13C NMR Spectra for a series of 11 substituted cyclobutanes derived from photodimerization of benzocycloalkenes were recorded. Comparison of the carbon chemical shifts for the head‐to‐head and head‐to‐tail cis‐syn‐cis and cis‐anti‐cis isomers reveals shielding trends which should facilitate structural and stereochemical assignments for related compounds. The head‐to‐head isomers show a larger separation of cyclobutane carbon resonances than the head‐to‐tail isomers. The cis‐syn‐cis isomers relative to the cis‐anti‐cis isomers exhibit distinctive upfield shifts of all carbon resonances, except those of aromatic carbons ortho to alkyl‐substituted aromatic carbons.

Dauphin, G.; Cuer, A.

doi: 10.1002/mrc.1270121003pmid: N/A

Une étude par spectroscopie 13C d'une série de composés méthylés soufrés est réalisée. Les effets des fonctions soufrées –SH, –SMe, –SSMe, –SSEt, –SSMe, –SC(O)Me, –SC(S)Me sur le déplacement chimique du carbone méthylique sont examinés. Les déplacements chimuques 13C d'une série de thio et dithioesters méthyliques aliphatiques sont comparés à ceux des esters correspondants et reliés aux propriétés chimiques.

Browne, L. M.; Klinck, R. E.; Stothers, J. B.

doi: 10.1002/mrc.1270121004pmid: N/A

The 13C spectra of a series of 21 cis‐decalins, 17 of which bear 10‐methyl substituents, have been recorded to examine geometrical and conformational effects on the 13C shieldings. Although the data for a few of the simpler examples have been reported, these compounds were examined to obtain results for a common medium and temperature. All of the derivatives are conformationally mobile and their spectra were examined as a function of temperature to obtain shieldings representative of the slow exchange limit. The examples include compounds which populate both available chair‐chair conformations equally, some which exhibit a preference for one of these conformations and some which exist essentially in a single conformation. The data for the latter group combined with the observed temperature dependencies and results for other decalin systems led to specific assignments for each carbon. The internal consistency of the entire body of data offers strong support for these assignments. The conformational preferences observed for a number of decalones and Δ3‐10‐methyldecalin derivatives are discussed.

Friebolin, H.; Schilling, G.; Pohl, L.

doi: 10.1002/mrc.1270121005pmid: N/A

Mit Hilfe des Klärpunktes von Flüssigkristallen kann im Kernresonanzspektrometer die Probentemperatur sehr exakt bestimmt werden. Das Verfahren ist für 1H‐ und 13C‐NMR‐Messungen geeignet und um den Faktor 5 genauer als die bisher bekannten. Bei 1H‐Messungen liegt der Fehler bei ±0,2°C, bei 13C‐NMR‐ Messungen bei ±0,3°C. Folgende Untersuchungen wurden durchgeführt: überprüfung der Ethylenglykol‐Eichgeraden, Eichung der Skala von NMR‐Temperatur‐Regelgeräten, Bestimmung des Temperaturgradienten in NMR‐Proben, Abhängigkeit der Probentemperatur vom Luftstrom und Beeinflussung der Probentemperatur durch Breitband‐ und Off‐Resonanz‐Entkopplung.

Bloxsidge, James P.; Elvidge, John A.; Jones, John R.; Mane, Ramachandra B.; Saljoughian, Manouchehr

doi: 10.1002/mrc.1270121006pmid: N/A

Small discrepancies between 3H and 1H chemical shifts in organic compounds led to the finding that the ratio of Larmor frequencies ωT/ωH depends on the carbon‐hydrogen bond hybridisation. The ‘best’ ratio for ghost referencing of 3H NMR spectra was then determined from measurements on purified partially tritiated TMS as 1.066639738±2 × 10−9. Some 3H isotope effects on chemical shifts are listed and the 3H isotope effect on the methylene geminal coupling constant in benzyl methyl sulphoxide is measured. Use of 2H in the measurement of 2J(HH) coupling constants has inherent disadvantages, overcome by use of 3H substitution.

Faure, Robert; Llinares, Jeanine; Vincent, Emile‐Jean; Elguero, José

doi: 10.1002/mrc.1270121007pmid: N/A

Les déplacements chimiques du carbone‐13 de la phényl‐1 pyrazoline‐2 et de vingt‐cinq N‐nitrophényl pyrazolines‐2, diversement substituées sur l'hétérocycle, ont été complétement attribués. Ces valeurs sont discutées en fonction des contraintes électroniques et stériques des différents substituants. Les effects stériques entrainent des modifications de la conformation aussi bien du groupement nitrophenyle, que du cycle pyrazoline‐2, ce qui explique les variations de certains déplacements chimiques.

Calvert, D. J.; Cambie, R. C.; Davis, B. R.

doi: 10.1002/mrc.1270121008pmid: N/A

The 13C NMR spectra of 20 polymethoxy‐ and/or methylenedioxyflavonols are reported. In key cases assignments have been made by examination of fully coupled spectra.

Gonzalez, Emmanuel; Faure, Robert; Vincent, Emile‐Jean; Espada, Modesta; Elguero, José

doi: 10.1002/mrc.1270121009pmid: N/A

Les déplacements chimiques du 13C de trente‐deux pyrazoles ont été mesurés dans le diméthylsulfoxyde hexadeutérié et l'hexaméthylphosphorotriamide. Nous avons déterminé l'influence respective des différents substituants par régression multilinéaire (substitutions par un méthyle et un amino sur les carbones de l'hétérocycle, et par un méthyle, un n‐butyle et un phényle sur l'azote). Le problème de la détermination des constantes d'équilibre tautomère, à partir des résultats de la RMN du 13C est discuté et illustré avec le cas des amino‐3(5) pyrazoles.

Romeo, G.; Aversa, M. C.; Giannetto, P.; Vigorita, M. G.; Ficarra, P.

doi: 10.1002/mrc.1270121010pmid: N/A

The sterochemistry of some 1,3‐dihydro‐2H‐1,4‐benxodiazepin‐2‐ones, employed as psychotherapeutic agents, is deduced by proton magnetic resonance using the paramagnetic shift reagent Eu(fod)3. the lanthanide induced shifts are computer simulated on the basis of the geometric parameters of the protons in different model structures, having intermediate conformations between a cycloheptadiene‐ and a cyclohepatatriene‐like system. N‐Desmethyldiazepam shows a conformational equilibrium between two pseudoboat forms, while the 1‐alkyl substituted derivatives exist, at room temperature, in olny one boat cycloheptatriene‐like conformation.