Molecular structures of fulvalenes derived from methylidenecycloproparenes: X-ray structure determinations and ab initio calculations

The X-ray crystallographic structures of crystalline fluorenylidenecycloproparenes 7 and 8 and of dibenzocycloheptatrienylidene 9 were investigated. Theoretical studies were used to analyze the structure, dipole moment, charge distribution and thermodynamic stability of the unidentified methylidenecycloopropabenzene 3, the derived parent tria-, penta- and heptafulvalene derivatives 4-6 and the crystalline derivatives 7,8 and 9. Results showed that hydrocarbons are polar and that the cycloproparenylidene moiety functions as electron donor.