ANISOTROPY OF INTERMOLECULAR INTERACTIONS FROM THE STUDY OF THE THERMAL-EXPANSION TENSOR

The anisotropy of the intermolecular interactions in the low-temperatu re ordered phases of three chemically and structurally related compoun ds [neopentylglycol, (CH3)(2)C(CH2OH)(2), pivalic acid, (CH3)(3)C(COOH ), and neopentylalcohol, (CH3)(3)C(CH2OH)], all of which display an or ientationally disordered high-temperature phase, has been shown by mea ns of the isobaric thermal-expansion tensor. The variation of the dire ctions of the principal components of the thermal-expansion tensor as a function of temperature, as well as the variation of its principal c oefficients, is evidence of the large differences in the intermolecula r interactions for each compound; or, more precisely, between the stro ng intermolecular hydrogen bonds and the weak van der Waals interactio ns. In addition, the differences in the hydrogen-bonding schemes expec ted a priori from the molecular structures of the studied compounds ha ve been enhanced. Finally, the volume expansivity as well as the packi ng coefficient have been analysed in the orientationally disordered hi gh-temperature phase of each of the three compounds.