The transannular interaction in [2.2]paracyclophane: repulsive or attractive?

The molecular structure and charge density distribution in the crystal of [2.2]paracyclophane derived from the high-resolution single crystal X-ray diffraction data at 100 K is reported together with ab initio calculations of this molecule. Analysis of the atomic, anisotropic displacement parameters in a "rigid-body" model approximation has revealed that the molecule is ordered in the crystal. Topological analysis of the electron density and potential-energy density-distribution functions has demonstrated that there is no "through-space" interaction between the rings in the molecule. The role of the ethylene bridges and distortion of the aromatic desks on the inter-ring interaction are discussed.