Dominant role of the pi framework in cyclobutadiene

The extrinsic antiaromaticity of archetypal cyclobutadiene (CBD) is addressed with particular emphasis on the alpha-pi separability problem. The study found that the one-electron MO picture cannot offer a satisfactory description of antiaromaticity, since both the alpha-MOs and pi-MOs energies contribute to E (d)(sub CBD) with an overwhelming influence of the alpha electrons.