Structural Changes on Twofold Oxidation of Tetrakis(dimethylamino)‐p‐benzoquinone: A Sterically Overcrowded Electron‐Rich “Chair” Compound Turns into a “Twist” Dicyanine Salt

On account of the four bulky (H3C)2N-substituents the tetrakis (dimethylamino)-p-benzoquinone molecule is electron-rich and sterically overcrowded. It has a chair conformation in which the OC groups are bent 12° above and below the central C4 plane. Oxidation with SbCl5/CH2Cl2 leads to a dication-bis (hexachloroantimonate), which is distorted to a twist conformation with dihedral angles of 35° by formation of two cyanine chains R2NCC(O)CNR; at the same time the quinone CC bonds are stretched from 137 to 146 pm (see structure on the right).