An X-ray investigation has been performed on five new 2,5-disubstituted 1,2,4-oxadiazoles with reversed structures containing 4-amylbiphenyl-, trans-4-amylcyclohexylphenyl- and 2-halophenyl-(hal = Cl, Br) as substituents. The aim was to confirm the data about the phase sequence, obtained via polarizing microscopy and differential scanning calorimetry, and to measure the structural parameters. Through X-ray diffraction technique, all substances showed only the nematic mesophase. Moreover, it was proved that some enthalpy variations previously attributed to crystal-crystal transitions are in fact due either to the rearrangement of the lattice or to the coalescence of the grains. However, for some substances, a second crystalline form C′ appeared at the melting point, on cooling from the isotropic phase. C′ turned out to be different from the starting form C1 of the sample, which had no any thermal cycle before.
X-ray investigation of new isomeric oxadiazoles / Francescangeli, Oriano; L. A., Karamysheva; S. I., Torgova; A., Sparavigna; A., Strigazzi. - 3319:(1998), pp. 139-144. (Intervento presentato al convegno Liquid Crystals: Chemistry and Structure tenutosi a Zakopane, Poland nel 3-8 March 1997) [10.1117/12.301271].
X-ray investigation of new isomeric oxadiazoles
FRANCESCANGELI, ORIANO;
1998-01-01
Abstract
An X-ray investigation has been performed on five new 2,5-disubstituted 1,2,4-oxadiazoles with reversed structures containing 4-amylbiphenyl-, trans-4-amylcyclohexylphenyl- and 2-halophenyl-(hal = Cl, Br) as substituents. The aim was to confirm the data about the phase sequence, obtained via polarizing microscopy and differential scanning calorimetry, and to measure the structural parameters. Through X-ray diffraction technique, all substances showed only the nematic mesophase. Moreover, it was proved that some enthalpy variations previously attributed to crystal-crystal transitions are in fact due either to the rearrangement of the lattice or to the coalescence of the grains. However, for some substances, a second crystalline form C′ appeared at the melting point, on cooling from the isotropic phase. C′ turned out to be different from the starting form C1 of the sample, which had no any thermal cycle before.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
