“…(26,73) The o-d transition corresponds to an equilibrium between the ordered phase at low temperatures and the following disordered phase: (i) orthorhombic β(Fmmm) (15,17,37,39,40,49) for the odd-numbered C 9 to C 25 : (7) in this structure, the stacking mode of the molecular layers along the long crystalline axis c corresponds to the orthorhombic (or hexagonal) ABAB sequence of crystalline planes (00 ), but the molecules orientate themselves in a disorderly manner around their long axis according to the two positions defined in the ordered structures, so that all occupancies by the molecules become equivalent in the A and B crystallographic planes by this "disorder in the molecular orientation" and lead to the centered-face space group denoted Fmmm in the Hermann-Mauguin symbols; (80) (ii) rhombohedral α-RII (R3m) for the even-numbered C 22 to C 26 : (15,17,37,39,40,49) in this structure which has the rhombohedral space group denoted R3m in the Hermann-Mauguin notation, (80) the stacking mode of the molecular layers (00 ) corresponds to the ABC rhombohedral sequence in which the molecules are probably in rotation around their axis. (49,77) In addition to this movement, defects appear in the molecular chains that lead to non-planar conformers which can be observed by infrared and Raman spectrometries.…”