About the Antiaromaticity of Planar Cyclooctatetraene I thank Jens Panitzky for the additional DFT calculations, and Professor Jay Siegel, La Jolla, CA, and Professor Otto Ermer, Cologne, for helpful comments.

A negligible antiaromatic destabilization is found in planar D4h 1,3,5,7-cyclooctatetraene with alternating bond lengths. The same is also true for the delocalized D8h structure, which has a stabilization energy of only 3–4 kcal mol−1. According to quantum-chemical calculations, the ground state of 1 is expected to be the planar C2v-symmetric (1,1) singlet diradical 1′.