The title compound, C8H10O2, was prepared from diacetyl by a high temp
erature and pressure reaction. Pseudosymmetry in the structure results
in diffraction symmetry enhancement for half the reflections and the
possibility of twinning and stacking faults. The structure consists of
two independent but pseudosymmetrically-related P2(1)/c substructures
, each having centrosymmetric molecules on centres of inversion which
are strongly hydrogen bonded to symmetry-related molecules to form lay
ers perpendicular to c. The structure may be described as an occupanc
y modulation, ordering a disordered parent structure in Pnma symmetry
to form, upon change of axes, the P2(1)/c structure reported. The hydr
oxyl H atoms have two site options corresponding to alternative hydrog
en-bonding patterns and the methyl H atoms in one substructure are rot
ationally disordered.