ISSN:
1573-1111
Schlagwort(e):
thiourea inclusion compounds
;
2H-NMR
;
13C-NMR
;
solid state NMR
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Chemie und Pharmazie
Notizen:
Abstract Solid state 13C-MAS and 2H-NMR investigationshave been performed on the bromo-cyclohexane/thiourea inclusion compound.The main objective of this study was the evaluation of the molecularfeatures of the guest molecules and their changes over a large temperaturerange (100 K 〈 T 〈 350 K). Particular emphasis was placed on themolecular behaviour in the vicinity of a solid–solid phase transitionat T = 237 K and in the low temperature phase, which was hitherto unknown.The 2H-NMR lineshape and relaxation studies reveal that, inthe low temperature phase, restricted but fast overall motions (MHz to GHzregion) of the guest molecules are dominant and reflect the distortedsymmetry of the thiourea channels. On heating above the solid–solidphase transition almost unrestricted overall motions appear, together with alarge degree of orientational disorder at higher temperature. Furthermore,the ring interconversion process presents a major relaxation process in theMHz region. The conformational order is unusual in the sense that the axialconformational state of the guest molecules is stabilized in the thioureachannels. It turns out that this unique property is also preserved in thelow temperature phase.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1023/A:1007913619221
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