CRYSTAL-STRUCTURE OF CHOLESTERYL OCTANOATE

Crystals of cholesteryl octanoate (C35H60O2) are monoclinic, space group P21, with a = 12.80(3), b = 9.20(2), c = 14.12(3) A ̊, β = 93.81(3)° and 2 molecules per unit cell. The structure has been determined by Patterson rotation and translation methods from the X-ray intensities (Mo-Kα radiation) of 1320 reflections (sinθ/λ < 0.59 A ̊-1) measured with a diffractometer. Refinement by block diagonal least squares and Fourier methods gave R = 0.096. The molecules are arranged in monolayers with their long axes antiparallel and severely tilted (28°). There is a close packing of cholesteryls within the monolayers, but the octanoate chains which form the layer interface regions are conformationally and thermally disordered. The crystal structure is quite different from that of cholesteryl nonanoate, as expected from the discontinuity in thermodynamic properties and phase behaviour which occurs at this point in the homologous series. © 1979.