Crystal and molecular structure of Z- and E-1,2-dichloro-1,2-bis(2-chlorophenyl)ethylene. An X-ray and NMR study

Abstract

Abstract: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 bondangle 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.Key words: chlorostilbenes, overcrowded molecules, X-ray structure, conformations, NMR spectroscopy. Ses molCcules existent dans une symttrie dictte par sa cristallographie. Dans les deux isomkres, les noyaux phtnyles sont approximativement perpendiculaires au plan moyen de 1'Cthyltne. Dans I'isomere Z, les atomes caractensant ce plan prtsentent des deviations significatives par rapport h la plankite. Dans les deux structures, on a observe des distorsions marqutes dans les angles de liaison des carbones de 1'Cthkne. On a dktermin6 les spectres RMN du 'H et du l3c et les deplacements chimiques, particulikrement du 'H, sont divists en deux rtgions spectrales bien distinctes. A basse temperature, dans chacun des composts, on a observt deux isomkres conformationnels qui different par l'orientation relative des liaisons C-C1 par rapport aux noyaux phtnyles.

1,1,2,2-Tetrachloro-1,2-diphenylethane

“…Halogenated hydrocarbons are known for their toxic effects, and some of these compounds are suspected of having human carcinogenic activity (Cornia et al, 1993). The title compound, (I), and its derivatives constitute an important class of halogenated hydrocarbons whose internal rotation processes and conformational preferences have been studied by NMR and X-ray methods (Antolini et al, 1995). In this context the crystal structure of (I) is reported here.…”