Electronic nature of planar cyclobutenyl dication derivatives.

The cyclobutadiene dication was not experimentally characterized to the date. However, some of its derivatives were. Most of them have planar geometry, but tetramethylcyclobutadiene dication has a nonplanar geometry according to ab initio calculations. From the atoms in molecules (AIM) theoretical analysis, common electronic features for the planar and puckered cyclobutenyl dication derivatives were observed. The planar cyclobutenyl dication derivatives have bond order of chemical bonds in the ring close to unity and relatively small electronic density in the ring. The puckered cyclobutadiene dication and its puckered derivatives have relatively high electronic density in the ring.