CRYSTAL-STRUCTURE OF 9-HYDROXYPHENALENONE - VERY SHORT INTRA-MOLECULAR HYDROGEN-BOND SYSTEM

9-Hydroxyphenalenone (C3H8O8) crystallizes in the monoclinic system with lattice constant a = 8.8941 (2) A,b = 28.8159 (4) Å, c = 7.2117 (2) Å,β = 97.937 (1)°,and eight molecules in the unit cell. The space group is P21/c. The structure was solved by direct methods and refined by the method of least squares. The final indicator R = 0.068 for the 2270 reflections with |Fobsd|2 > 3σ|Fobsd|2. One of the two independent molecules is disordered leading to reduced dimensional accuracy. The other molecule has effective mm2 symmetry. The intramolecular O…O distance is 2.486 (4) Å; all dimensions in this molecule are consistent with a symmetric hydrogen bond or a situation in which the hfydrogen is undergoing exchange between two closely spaced equilibrium positions. The disordered molecule equally occupies two major orientations, approximately related by a 120° rotation in the molecular plane. Diffuse X-ray scattering indicates appreciable short-range correlations between the orientations of the disordered molecule. Two phase transitions have been detected: one is at 252 K, the other occurs in the range 330-395 K. © 1979, American Chemical Society. All rights reserved.