TOPOLOGICAL ANALYSIS OF EXPERIMENTAL ELECTRON-DENSITIES .1. THE DIFFERENT C-C BONDS IN BULLVALENE

The static electron density based on the rigid-pseudoatom model is ext racted from low-temperature, high-resolution X-ray diffraction data of bullvalene (tricyclo[3.3.2.0(2.8)]deca-2,5,8-triene). A comparative a nalysis of the anisotropic displacement amplitudes based on this and t he earlier neutron diffraction study reveals bias in the neutron param eters possibly due to inadequate treatment of extinction. The topologi cal properties of the experimental charge distribution are compared to those obtained from wave functions at different levels of theory. The agreement reached is excellent, especially for the values of the elec tron density at the bond critical points. The four different e-C bond types can clearly be established. All ring and cage critical points ca n also be located, confirming the reliability of the experimental dens ity even far away from the nuclei. The model dependence of the topolog ical properties is also discussed, and the importance of the proper tr eatment of the hydrogen atoms is shown.