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Crystal structure of cyclobutane at 117 K


Lehmann,  C.W.
Institut fiir Kristallographie, Freie Universitat Berlin, D- 1000 Berlin 33, Germany;
Service Department Lehmann (EMR), Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Stein, A., Lehmann, C., & Luger, P. (1992). Crystal structure of cyclobutane at 117 K. Journal of the American Chemical Society, 114(20), 7684-7687. doi:10.1021/ja00046a012.

The crystal structure of cyclobutane was determined from X-ray diffraction data at 117 K. The crystal used was grown by sublimation. Since a rotationally-disordered high-temperature phase is present over a temperature range of 38 deg, no crystals could be obtained from the melt. The cell dimensions at 117 K are a = 6.742 (4)Å, b = 4.204 (4)Å, c = 6.917 (4)Å beta = 90.17 (4)°, space group I2/m, Z = 2. The space group symmetry requires the space- or time-averaged molecules to have C2h(2/m) symmetry. The carbon atoms show initially large anisotropic displacement parameters perpendicular to the mirror plane. Two explanations are discussed. The first is based on earlier investigations and assumes the time-averaged molecules to undergo puckering motions, which is established for the gas phase and the solid state. The other explanation which is more compatible with the experimental data is a statistical disorder of bent molecules. The latter results in a dihedral angle of 31 (2)°, which agrees with most other investigations.