Crystal and molecular structure of a root inhibitor fromEucalyptus grandis, 4-ethyl-1-hydroxy-4,8,8,10,10-pentamethyl-7,9-dioxo-2,3-dioxabicyclo [4.4.0]decene-5

The crystal structure of C₁₅H₂₂O₅, a root inhibitor isolated from adult leaves ofEucalyptus grandis, has been determined by direct methods with Cuk diffractometer data and refined by full-matrix least-squares calculations toR = 0·046 for 1829 statistically significant reflexions. The compound, a racemate, crystallizes in the monoclinic space groupP2₁/c, with unit cell dimensionsa = 11·767,b = 12·063,c = 10·906 Å, = 103·2° andZ = 4. The molecular skeleton consists of a 2,3-dioxabicyclo4.4.0]decene system with one hydroxyl, two carbonyl, one ethyl and five methyl side groups. The dihedral angle at the peroxide bond is 76·8° and the O-O bond distance is 1·480 Å. The molecules are linked in the c direction by hydrogen bonds between the hydroxyl group and one of the carbonyl oxygen atoms.The author is grateful to Professor W. D. Crow for suggesting the problem and for crystals ofG1, to Dr A. McL. Mathieson (Division of Chemical Physics, C.S.I.R.O.), in whose laboratory the data were collected, and Mr J. Fridrichsons for their advice and continued interest, to Dr W. A. Denne (Division of Chemical Physics, C.S.I.R.O.) and Mr B. J. Poppleton (Division of Forest Products, C.S.I.R.O.) for help and advice in the data collection and for the use of data reduction programs and to Dr D. A. Wright (Chemical Physics Group, Department of Supply) for several computer programs used in this work.