55 research outputs found
ChemInform Abstract: N-OXIDE 37. MITT. UV- UND ESR-UNTERSUCHUNG VON 2,3,4,5-TETRAPHENYLPYRROL-1-OXYL
EPR study of pyrrolylâ1âoxyl and 3âpyrrolinylâ1âoxyl radicals
Pyrrolylâ1âoxyl, 3âphenylpyrrolylâ1âoxyl and a number of deuteriumâsubstituted derivatives were generated by hydrogen abstraction from the corresponding Nâhydroxypyrroles, and observed by EPR spectroscopy. They were all transient with lifetimes †10â2 s. The hyperfine splittings showed that unpaired spin was delocalized around the fiveâmembered ring with significant density at Nâ1, Câ3 and Câ4, but very low density at Câ2 and Câ5. NâHydroxpyrrole and pyrrolylâ1âoxyl were studied by the semiâempirical AM1 method, and the radical by the INDO method. The transient pyrrolinylâ1âoxyl was also generated from the corresponding Nâhydroxypyrroline and observed by EPR spectroscopy.</p
Small angle neutron scattering study of steroidal gels
Gels formed by a dilute solution of modified steroids in cyclohexane have been studied by Small Angle Neutron Scattering. The presence of very long objects associated with the gel network is clearly demonstrated. Contrast variation experiments show that these objects are essentially composed of steroid molecules. Absolute intensity measurements, and fits of the full scattering curves using models, suggest that these objects are chiral, possibly symmetrical double helices of diameter ca. 100 Ă
. It is suggested that the « contact points » in the network of the gel are achieved by coiling together two or more long objects over distances rather large compared to the diameter. The influence of the existence of such overlapping on the shape of the experimental scattering curves is discussed.Des gels formĂ©s Ă partir de solutions diluĂ©es dans le cyclohexane de stĂ©roĂŻdes modifiĂ©s, sont Ă©tudiĂ©s par diffusion de neutrons aux petits angles. La prĂ©sence d'objets trĂšs longs associĂ©s avec le rĂ©seau du gel est mise clairement en Ă©vidence. Des experiences de variation de contraste montrent que ces objets sont essentiellement composĂ©s par des molĂ©cules stĂ©roĂŻdes. Des mesures d'intensitĂ©s absolues et l'ajustement des courbes de diffusion Ă des modĂšles simples suggĂšrent que ces objets sont chiraux, probablement des doubles hĂ©lices symĂ©triques de diamĂštre d'environ 100 Ă
. On suggÚre que les « points de contacts » entre objets sont formés en torsadant deux ou plusieurs de ces longs objets sur des distances relativement grandes par rapport au diamÚtre. L'influence de ce recouvrement des objets sur la forme des courbes de diffusion est discutée
Nitroxydes LXXVIII : rĂ©sonance paramagnĂ©tique Ă©lectronique de radicaux pyrryles et nitroxydes pyrroliques. Calcul des densitĂ©s de SPIN et dĂ©termination des paramĂštres ÏÏ
Il est possible d'obtenir des corrĂ©lations linĂ©aires entre les densitĂ©s de spin calculĂ©es par des mĂ©thodes simples (mĂ©thode de HĂŒckel pour les nitroxydes pyrroliques, indoliques et car- bazoliques et mĂ©thode de Mac Lachlan pour les radicaux pyrryles), et les couplages hyperfins de l'azote et des divers protons de la molĂ©cule
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