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  • Author: Albert Schneider x
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Defokussierte elektronenmikroskopische Aufnahmen von Nickelschichten, die in Gegenwart organischer Fremdstoffadsorbate elektrolytisch abgeschieden wurden, zeigen starke Punktkontraste. Verschiedene elektronenoptische Beobachtungen, ergänzende spektralphotometrische Messungen und lichtoptische Modellversuche lassen den Schluß zu, daß die Punkte durch Phasenkontrast sichtbar gemachte einzelne Moleküle oder einige wenige Moleküle enthaltende Fremdstoffeinschlüsse sind.

Abstract

NMR spectra of several cyclohexenone epoxides obtained by oxygenation of 4-R-2,6-di-tert-butylphenols have been assigned, using substituent induced shifts, offresonance and C - H single-frequency-decoupling techniques, as well as completely C - H coupled spectra. For the -butyl signals the following sequence rules are relevant: methyl carbons and protons = δtBu-C-olefinic(sp2) > δtBu-C-oxirane(sp3) ≥ δtBu-C-OH(sp3); quaternary carbons = δtBu-C-OH(sp3) > δtBu-C-olefinic(sp2) > δtBu-C-oxirane(sp3). In these compounds, the oxirane oxygen causes a highfield shift of the signal of the quaternary C-atom of the feri-butyl group as compared with the influence of a hydroxy group.

Abstract

The phase behaviour of a new liquid crystal, belonging to the series l-[4-n-alkyl-biphenyl]-2-[4-isothio-cyanato-phenyl]ethane (nTPEB), n = 10, has been investigated with differential scanning calorimetry at ambient and high pressure. The phase behaviour depends on the thermal treatment. Phase transition temperatures have been determined as a function of pressure up to 300 MPa. No pressure-induced or pressure-limited phases are observed in this pressure range. Enthalpy-and volume-changes accompanying the phase transitions have been calculated using the Clausius-Clapeyron equation.

Abstract

Densities have been determined for two 5-n-alkyl-2-(4-isothiocyanatophenyl)-1,3-dioxanes (6DBT, 10DBT), 4-n-tetradecyl-4'-cyanobiphenyl (14CB), 4-n-octyl-4'-thiocyanatobiphenyl (8BT) and two laterally aryl-branched mesogens 4-cyanobenzyl 5-(4-n-octyloxybenzoyloxy)-2-undecyloxybenzoate (4CNOUB), 3-cyanobenzyl 2,5-bis(4-n-octyloxybenzoyloxy)benzoate (3CN-BOB). The densities have been measured in the isotropic, nematic (only 3CNBOB) and smectic phases with a vibrating tube densimeter. The densities decrease with increasing alkyl chain length within a homologous series. Furthermore the enthalpy changes accompanying the phase transitions have been determined by DSC.