Crystal and molecular structure of 2- and ethylene. An X-ray and NMR study

The crystal structures of the title compounds were determined by single crystal X-ray diffraction techniques. The molecule of the Z isomer, which crystallizes in the monoclinic space group C21c with Z= 4 in a cell of dimensions a = 14.891 (2), b = 10.780(2), c = 8.769(1) A, P = 97.47(2)", V = 1395.7(7) A3, has crystallographic twofold symmetry. The E form crystallizes in the orthorhombic space group Pbca with a = 11.730(1), b = 6.932(1), c = 16.841(1)A, V= 1369.4(2) A3, and Z = 4. Its molecules have crystallographically dictated symmetry. In both isomers the phenyl rings are roughly perpendicular to the average ethylene plane. The atoms characterizing this plane show significant deviations from planarity in the Z isomer. Marked bond- angle distortions at the ethene carbons of both structures are observed. The 'H and I3c NMR spectra of the compounds were measured and, particularly in the case of the 'H chemical shifts, fall into two quite separate spectral regions. At low temperature, two conformational isomers, those with different relative orientation of the C-C1 bonds of the phenyl rings, are observed in the spectrum of each compound.