DIRECT PHASE DETERMINATION IN ELECTRON CRYSTALLOGRAPHY - THE CRYSTAL-STRUCTURE OF AN NORMAL-PARAFFIN

Crystal structure analyses of polymethylene compounds via direct phasing methods are notoriously difficult because of the dominance of the diffraction intensity by the scattering from polymethylene lattice. However, by combination of high resolution low-dose images with conventional direct phasing via structure-invariant relationships, one can assign phase values to the most important regions of the diffraction pattern (i.e. "lamellar" and "polyethylene" reflections, respectively). As demonstrated here with experimental data from the epitaxially crystallized paraffin, n-hexatriacontane, the phased observed structure factor magnitudes produce an electrostatic-potential map with atomic positions identical to the previously published X-ray crystal structure. © 1990.