A combined crystallographic, thermal, Raman and computational study on polymorphism and phase transition in 1-(4-hexyloxy-3-hydroxyphenyl)ethanone

Abstract

The crystal structure of the triclinic polymorph of 1-(4-hexyloxy-3-hydroxyphenyl)ethanone, C14H20O3, differs markedly from that of the orthorhombic polymorph [Manzano et al. (2015). Acta Cryst. C71, 1022-1027]. The two molecular structures are alike with respect to their bond lengths and angles, but differ in their spatial arrangement. This gives rise to quite different packing schemes, even if built up by similar chains having the hydroxy-ethanone O - H...O hydrogen-bond synthon in common. Both phases were found to be related by a first-order thermally driven phase transformation at 338-340K, which is discussed in detail. The relative stabilities of both polymorphs are explained on the basis of both the noncovalent interactions operating in each structure and quantum chemical calculations. The polymorphic phase transition has also been studied experimentally by means of differential scanning calorimetry (DSC) experiments, conducted on individual single crystals, Raman spectroscopy and controlled heating under a microscope of individual single crystals, which were further characterized by powder and single-crystal X-ray diffraction.A triclinic phase of 1-(4-hexyloxy-3-hydroxyphenyl)ethanone is described and compared with the previously reported orthorhombic phase. The polymorphic phase transition involving the structures is analyzed.