Interpretation of rotational disorder in crystalline paraterphenyl in terms of non-bonded interactions

Abstract

On cooling crystalline paraterphenyl from room temperature to ∼110 K, the unit cell dimensions a and b each double and the space-group changes from P2₁/a to P1. The transition involves the so-called phenomenon of “rotational disorder” in which the individual molecules become non-planar. By evaluating, in pairwise fashion, the interactions between non-bonded atoms, it is possible to elucidate the nature of this transition, and in particular, to determine semi-empirically the conformations of the non-planar molecules in, and the lattice parameters of, the low-temperature stable phase. The agreement between the computed and recently determined (X-ray) values is very good. The existence of additional, rotationally disordered phases is also predicted.