Crystal structures of 1-hy-droxy-4-prop-yloxy-9,10-anthra-quinone and its acetyl derivative

1-Hy-droxy-4-prop-yloxy-9,10-anthra-quinone, C₁₇H₁₄O₄, (I), and its acetyl derivative, 4-acet-yloxy-4-prop-yloxy-9,10-anthra-quinone, C₁₉H₁₆O₅, (II), were synthesized from the commercially available dye quinizarin. In both compounds, the anthra-quinone frameworks are close to planarity. There is a large difference in the conformation of the prop-yloxy group; the mol-ecule of (I) adopts a gauche conformation [O-C-C-C = -64.4 (2)°], although the mol-ecule of (II) takes a trans-planar conformation (zigzag) [O-C-C-C = 176.1 (3)°]. In the mol-ecule of (I), there is an intra-molecular O-H⋯O hydrogen bond. In both crystals, the mol-ecules are linked by C-H ⋯O hydrogen bonds. A difference in the mol-ecular arrangements of (I) and (II) is found along the stacking directions.