Alcoyl-gluco-alcaloides: nouveaux composes isoles de pauridiantha lyalii brem (rubiacees)

La structure destrans fe´ruloyl-6′ ettrans sinapoyl-6′ lyaloside, isole´s des feuilles dePauridiantha Lyalii, ae´te´de´termine´e par de´gradation chimique et par spectroscopie (Masse, RMN¹H et¹³C). Ces compose´s font partie d'un groupe structural caracte´rise´par un enchai?nement alcaloide-monoterpe`ne-ose-acide (C<sub>6</sub>-C<sub>3</sub>), groupe dont un seul repre´sentant semble avoire´te´isole´jusqu'a`pre´sent. Leur fonction dans le ve´ge´tal est discute´e.     

Ion photodesorption from argon multilayers

Received: 16 June 1997/Accepted: 26 October 1997     

On the use of photoelastic composite models

Emphasis in the paper is placed on establishing the validity of employing photoelastic composite models to study assumptions used in composite-material analysis. Two approaches for the derivation of material constants for plane-stress layered composite materials are presented. Basic assumptions of the theories are studied. The theoretical and experimental equivalent moduli for test specimens loaded in tension and in shear are also compared.     

Ba(SCN)2(H2O) complex of the cis-syn-cis isomer of 2,5,8,15,18,21-hexaoxatricyclo[20,4,0,09,14]hexacosane(dicyclohexyl-18-crown-6) [Ba(SCN)2(H2O)(C20H36O6)]

The structure of the title compound has been redetermined. Hydrogenation of dibenzo-18-crown-6 yields two conformational isomers which were proposed to be the cis-syn-cis and the cis-trans-cis isomers of dicyclohexyl-18-crown-6. The previous study had established that the title complex contains the ligand which has the cis-syn-cis conformation but had resulted in some inaccurate bond lengths and also in an uncertainty regarding the presence of a water of hydration in the crystal. This study confirmed the report of the general conformation of the complex, resulted in more precise bond lengths and clearly established that a water of hydration was present at the crystal.     

A comparison of classical and quantum-mechanical ‘ring-current’ theories

The proton resonance spectra of a series of 2,7-disubstituted-4,5-bis(2-pyridyl)phenanthrene-3,6-diols are examined with emphasis on the shielding effects produced by aromatic ‘ring currents.’ In this series, two pyridine rings are rigidly held less than 3.4 Å apart and with considerable overlap. The ‘ringcurrent’ shieldings found for above-the-plane positions are in good agreement with the Johnson-Bovey theory, whereas a recently proposed quantum-mechanical theory underestimates the shieldings by a factor of nearly three.     

Zur Strukturanalyse von stellungsisomeren, partiell substituierten Phosphornitridchlorid-(PNCl2)3-Derivaten

Zusammenfassung Der Einsatz von 4,4-Dihydroxymethylcyclohexen (A) führt zu einem neuen chemischen Verfahren zur Strukturaufklärung von stellungsisomeren, partiell substituierten Phosphornitridchlorid-Derivaten. Die Reaktion von (A) mit P₃N₃Cl_nR_6-n verläuft unter sehr milden Bedingungen. Die massenspektrometrische Untersuchung der Reaktionsprodukte gestattet die Unterscheidung zwischen geminaler und vicinaler Anordnung der Liganden R.Vortrag anläßlich der Tagung über Strukturanalyse anorganischer und organischer Verbindungen, Lindau, 10.–12. 6. 1974.