Zur Konformation des Bicyclo[2.2.2]octan‐Systems

TLDR: In this article, the structure of the bicyclo [2.2]-octane (BCO) skeleton has been solved with the help of direct methods and refined by full-matrix least-squares analysis of the three-dimensional intensity data.

Abstract: Crystals of bicyclo [2.2.2] octane-1, 4-dicarboxylic acid are monoclinic, a = 6.01 A, b = 16.73 A, c = 10.29 A, β = 115.08°, space group P21/c, with 4 molecules in the unit cell. The structure was solved with the help of direct methods and refined by full-matrix least-squares analysis of the three-dimensional intensity data. Within experimental error the bicyclo [2.2.2]-octane (BCO) skeleton has apparent D3h-symmetry, corresponding to the totally eclipsed conformation. Analysis of the thermal ellipsoids in terms of the translational and rotational motion of the BCO skeleton leads to an r.m.s. amplitude of 5.9 ± 0.2° for rotation about the threefold axis. On the assumption that the bond lengths remain effectively constant during a torsional vibration of BCO, the potential energy surface has been calculated for a range of semi-empirical potential functions. These calculations show that the energy minimum may be slightly displaced from D3h symmetry, but if so the barrier between the two such equivalent minima is only about 0.1 kcal mole−1. The energy eigenvalues and eigenfunctions for a typical variation of potential energy vs torsion angle have been calculated. From the form of the eigenfunction of the ground vibrational state we conclude that BCO has effective D3h symmetry at all temperatures as far as diffraction methods are concerned.