Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

Structural and thermodynamic insights are reported for the series of fluorinated alcohols {oFTOH; CF3(CF2)nCH2OH, with n = 5 12}, with the objective of comparing the phase behaviour of perfluorinated compounds with the analogous linear alkanes and alcohols. As expected the higher vibrational contribution of the CF2 groups contributes for the higher heat capacities of the perfluorinated compounds. Concerning the fusion/sublimation equilibria, fluorination of the alcohols decreases DH and DS of phase transitions. Compared to the regular CH2 alkyl chain structure, the less symmetric CF2 spiral conformation is characterized by a less efficient molecular alignment in crystal packing, thus explaining the lower DH. The lower internal rotational barrier associated with the CH2 alkyl chains of n-alkanes/alcohols, when compared to CF2 chains, contributes to the larger values of DS observed. Regarding the vaporization equilibria, fluorination leads to greater values of DS, which are explained by the larger translational entropy of the heavier perfluoroalcohols, an effect that is more important in the gas than in the liquid phase.