STRUCTURES OF STERICALLY OVERCROWDED OR CHARGE-PERTURBED MOLECULES .8. STRUCTURAL-CHANGES ON TWOFOLD OXIDATION OF TETRAKIS(DIMETHYLAMINO)-PARA-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-degrees 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-degrees by formation of two cyanine chains R2NC-C(O)-CNR2+; at the same time the quinone C = C bonds are stretched from 137 to 146 pm (see structure on the right). [GRAPHICS]