Crystals of the title compound, C13H120, are orthorhombic, space group Pbca, a=19-750 (3), b= 13"448 (3), c = 7"422 (2)/~ and Z= 8. The structure was solved by the direct method and refined by the full-matrix least-squares method. The final R value was 0.056 for 1222 observed reflexions. The sevenmembered ring of the molecule takes a shallow, twisted boat form with a bow angle of 10.8 ° and a stern angle of 4-8 °. Significant elongation of the single bonds neighbouring the carbonyl group is observed [C(1)-C(2) 1.477/~.], primarily due to the non-bonded repulsions between the carbonyl O and methyl C atoms.