The electronic structure of singlet cyclopentadienylidene

We have carried out ab initio multiconfigurational self-consistent field calculations on the lowest singlet state of the carbene C5H4. We find that there are, along a restricted geometry deformation coordinate, two local energy minima corresponding to localized and delocalized π bonds having 4π and 6π electrons, respectively. The role of 4n + 2 resonance in determining the nature of the electronic structure and reactivity of this carbene is analyzed and compared with that of other carbenes.