STRUCTURAL INTERACTIONS BETWEEN N-PARAFFINS AND THEIR PERDEUTERATED ANALOGS - BINARY COMPOSITIONS WITH IDENTICAL CHAIN LENGTHS

Electron diffraction and calorimetric studies were made on perdeuterated n-paraffins and compared to the fully hydrogenated analogues. It is seen that the crystal structures of the respective molecules are identical with no measurable difference seen between their unit cell dimensions. As shown earlier, the incorporation of deuterium does not greatly change the molar transition enthalpy of the molecules. However, for a homologous series, perdeuteration lowers the chain length where the transition to a "rotator" phase vanishes. Otherwise, the chain disorder for the analogous compounds is identical when they are heated. Binary phase diagrams of equal chain length compositions are not only ideal for the phase boundary between the "rotator" phase and the melt, as found for all cosoluble n-paraffins, but also for the orthorhombic to "rotator" transition. These observations suggest that the dispersion forces for the two chemical species are very similar.