Structural Study of the Methylnaphthazarins. X-Ray Structure of the Tetramethylnaphthazarin, a Charge Transfer Complex

The synthesis and analysis by 1H NMR of the methyl substituted naphthazarins were attempted. The chemical shifts of the substituents and of the ring protons were compared with those in their diacetates and were then correlated with the quinonoid or benzenoid nature of the rings. X-Ray diffraction analysis of tetramethylnaphthazarin, 2,3,6,7-tetramethyl-5,8-dihydroxy-1,4-naphthoquinone, has shown that this exists, in solid state, as a centrosymmetric charge-transfer complex with itself. The compound crystallizes in the Ibamspace group, with an orthorhombic cell of dimensions a=17.479(1), b=9.983(1), c=6.752(1) Å, and four molecules in the unit cell. The crystal is built from molecules stacked up the c-axis and the interplanar distance between two overlapping molecules is 3.38 Å.