Crystals of the title compound, CaaHxxO2N, are orthorhombic, space group Fdd2, Z= 8, a=27.289 + 0.004, b = 13.108 + 0.005, c = 9-165 + 0.002/~, Dx = 1.362 g.cm -3. Data for 454 reflections were collected at room temperature on a Picker automated diffractometer. The structure was solved by direct methods, using a computerized multiple-solution procedure, and it was refined by full-matrix least-squares methods to a final R on F of 0"046, with 377 observed reflections. The average e.s.d.'s of the bond lengths and angles not involving hydrogen are about 0.008 A and 0.5 °, respectively. Bond lengths and angles were corrected for thermal motion. Some C-C single bonds are found to be significantly shorter than the normal C-C single bond length of 1.54 A. The shortening of the C-C bonds is explained by the conjugation of the C=O bond and C=C bond with the three-membered ring.