Conformation of the sesquiterpenoid zerumbone: X-ray crystallographic analysis of zerumbone 2,4-dinitrophenylhydrazone

The molecular geometry of the title compound, C15H22O, has been determined by X-ray diffraction. The double bonds in the 2,6,9,9-tetramethylcycloundeca-2,6,10-trienone ring have trans-stereochemistry. The conformation of the macrocycle differs from that found in several derivatives of humulene, C15H24, and is related to one of the low-energy conformations of cycloundecane. Force-field calculations indicate that this zerumbone conformation is of lower energy than the alternative humulene-like conformation. Crystallographic data are a = 12.619(2), b = 7.290(3), c = 23.422(3) Å, β = 98.06(1)°, 2 = 4, space group P21/c. Diffractometer intensity measurements were made with Cu-Kαradiation and least-squares adjustment of the atomic parameters converged at R 0.046 for 3 222 |F0| values.