Two polymorphs of 4‐propyl‐3,4‐dihydro‐2H‐naphtho[1,2‐b]pyran‐5,6‐dione

Two polymorphs of the title compound, C₁₆H₁₆O₃, have been obtained from the same solution. One polymorph, (I_m), crystallizes in the monoclinic space group P2₁, while the other, (I_o), crystallizes in the orthorhombic space group P2₁2₁2₁. The cell constants of the two polymorphs are surprisingly similar. Whereas the a and b axes are equal in the two structures, the c axis in (I_o) is twice as long as that in (I_m). The monoclinic angle β is 95.084 (9)° compared with 90° in the orthorhombic crystal system. The cell volume of (I_m) is almost exactly half of the cell volume of (I_o). The packing motifs are also very similar in the two structures. However, whereas the molecules in (I_m) are related by a twofold screw axis just in the direction of the b axis, in (I_o) there are twofold screw axes along all three directions of the unit cell.