QUINOID STRUCTURE OF DIAZINE RING IN 4-IMINECINNOLINES - CRYSTAL AND MOLECULAR-STRUCTURE OF 3-CARBAMOILO-1,4-DIHYDRO-4-IMINO-1-METHYLCINNOLINE

The very first 1-alkyl-4-iminocinnoline studied by X-ray diffraction s hows quinoid structure of diazine ring correlated with partial localiz ation of pi electrons in a fused benzene ring, similarly to phenomenon observed in 1-alkyl-4-cinnolinones. Surprisingly, the common bond has normal aromatic length of 1.398(7) Angstrom. Due to intramolecular hy drogen bond between 4-imine and 3-carbamoil substituents, the latter g roup is coplanar with aromatic system. In the crystal the molecules co nnected by intermolecular hydrogen bonds form layers perpendicular to [100] direction with stacking of the cinnolines rings. Separations of aromatic systems is about 3.5 Angstrom, i.e. a(0)/2.