Electron crystallography of the polymethylene chain. 1. The crystal structure of n-tritriacontane in the B-polymorph 1

The crystal structure of n-tritriacontane, n-C33H68, in its B-form, has been determined quantitatively from three-dimensional electron diffraction data from epitaxially oriented samples, based on four most densely populated, independent reciprocal lattice nets, with 001, as the tilt axis. When the selected area is small enough, contamination of zonal intensities from nearby reciprocal lattice nets, induced by irregular crystal bending, can be largely eliminated. Unit cell constants are: a = 7.53 Å, b = 4.99 Å, c = 88.44 Å, with β = 90.0°. The space group is most likely A21 am, although an equivalent model, based on an orthogonal Aa structure, will match the 59 unique structure factor values (R = 0.21). No evidence has been found for the twinned monoclinic structure proposed in earlier x-ray studies.