Studies on Disc-like Molecules

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Abstract
The heat capacity of benzene-hexa-n-hexanoate, C6(OCOC5H11)6, with a purity of 99.98 mole per cent has been measured between 13 and 393 K. Four phase transitions were found at 251.58 (Phase IV → III), 291.46 (III → II), 348.27 (II → I) and 368.74 K (Phase 1 → liquid). The enthalpy and entropy of these transitions were determined to be 25.66 kJ mol−1/102.67 J K−1 mol−1; 12.27/46.11; 16.26/46.68; and 33.50/90.86, respectively. These phase transitions are regarded as a kind of successive phase transitions: the conformational melting progresses from the periphery of a molecule into its inside each time a phase transition takes place. The infrared and far infrared spectra remarkably depend on temperature; the noticeable changes observed with increasing temperature are a smearing effect of the intramolecular vibrational modes and a reduction of the number of infrared active bands. The spectra of Phase I are substantially the same as those of the liquid, indicating rapid motions of the paraffinic chains in Phase I. The phase transitions can be seen very clearly under a polarizing microscope. The optical texture of Phase I seems to be of crystal rather than of liquid crystal. The highest temperature “solid” phase (Phase I) was concluded here to be a highly disordered crystalline phase concerning conformations of the paraffinic chains.