X-ray structure and charge density studies of 1,5-dimethyl-2,4,6,8-semibullvalenetetracarboxylic dianhydride in the temperature range 123-15 K

The structure of the bisannelated semibullvalene, which was previously thought to be in symmetrical homoaromatic ground state, was studied by ultralow-temperature diffraction experiments. High-resolution X-ray data obtained at 15 K afforded a detailed electron density distribution that permitted a full topological examination. Findings showed that in the solid state, the semibullvalene is not homoaromatic.