Bending of the CCH bond angle maintaining D-2d symmetry for COT leads to a partial rehybridization at carbon atoms which in consequence causes a significant decrease of bond length alternation and increase of planarization of the molecule. Analysis of the changes in exaltation of the magnetic susceptibility and NICS shows that the changes in pi-electron structure are dramatic, much greater than that observed for a similar deformation of benzene. (C) 2002 Published by Elsevier Science B.V.