Polymorphism of N-Alkanols: 1-Heptadecanol, 1-Octadecanol, 1-Nonadecanol, and 1-Eicosanol

The polymorphism of 1-heptadecanol (C 17 H 35 OH), 1-octadecanol (C 18 H 37 OH), 1-nonadecanol (C 19 H 39 OH), and 1-eicosanol (C 20 H 41 OH) has been studied by X-ray powder diffraction, differential scanning calorimetry (DSC), Raman scattering, and infrared spectroscopy (IR). At room-temperature two monoclinic forms, β and γ, are observed. For the n -alkanols with an even number of carbons the stable form is γ, whereas β is the stable form for the n -alkanols with an odd number of carbons. On heating, these phases transform to a monoclinic, rotator form R' IV at a few degrees below the melting point. A metastable β form is obtained by quenching from the melt for 1-octadecanol and 1-eicosanol, which is isostructural with the β-phase of the odd alkanols. Cell parameters, temperatures, and enthalpies of the transitions are reported.