Thermal expansion of β-succinic acid and α-adipic acid in relation to their crystal structures

Abstract

The thermal expansion quadrics of β -succinic acid and α -adipic acid have been determined by X-ray Weissenberg method. In adipic acid, X-ray measurements have been made between —100 and +100°C and in succinic acid between —150 and +130°C. In these monoclinic crystals, the minimum expansion corresponds to the c axis, which coincides with the direction of the hydrogen-bonded molecular columns. In other directions along which van der Waals forces prevail, thermal expansion is greater, being maximum perpendicular to the (100) planes, the direction of the obtuse bisectrix of the molecular packing angle. The thermal expansion is quantitatively explained by assuming an increase in the angular vibration of the molecules.