Polymorphism of Long-Chain Alkane-α,ω-Diols with an Even Number of Carbon Atoms

Abstract

Crystal structures of long-chain alkane-α,ω-diols with an even number of carbon atoms from 20 to 24 are determined. The molecular structures are similar to those of the lower homologues with an even number of carbon atoms analyzed previously; however, the methylene chain packings are different from each other. In the newly analyzed structure, it is found that the crystal structure type has an advantage in the close packing for the methylene part with increasing hydrophobic interactions. Crystal structures of a different polymorphic form in the even number of carbon atoms from 16 to 24 are also determined. The molecular and crystal structures are similar to those of an odd number of carbon atoms analyzed previously. However, the structures are slightly different from self-assembled multilayer structures whose models are derived from a grazing incidence synchrotron X-ray diffraction data. The carbon number starting to exhibit a polymorphic form coincides with that starting to show a rotator phase which are observed just below their melting points. From the viewpoint of the epitaxial growth at the surface and of the calculated density, it is found that the crystal structure of the polymorphic form has an advantage in exhibiting the rotator phase.