Anisotropy of Intermolecular Interactions from the Study of the Thermal-Expansion Tensor

Abstract

The anisotropy of the intermolecular interactions in the low-temperature ordered phases of three chemically and structurally related compounds [neopentylglycol, (CH₃)₂C(CH₂OH)₂, pivalic acid, (CH₃)₃C(COOH), and neopentylalcohol, (CH₃)₃C(CH₂OH)], all of which display an orientationally disordered high-temperature phase, has been shown by means of the isobaric thermal-expansion tensor. The variation of the directions of the principal components of the thermal-expansion tensor as a function of temperature, as well as the variation of its principal coefficients, is evidence of the large differences in the intermolecular interactions for each compound; or, more precisely, between the strong intermolecular hydrogen bonds and the weak van der Waals interactions. In addition, the differences in the hydrogen-bonding schemes expecteda priorifrom the molecular structures of the studied compounds have been enhanced. Finally, the volume expansivity as well as the packing coefficient have been analysed in the orientationally disordered high-temperature phase of each of the three compounds.