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Abstract. C15H2204, triclinic, P]" (from structure analysis), a=6"81 (1), b=8"80 (1), c=12.10 (2) /~, ~= 104.3 (3), fl=93"5 (3),),=98"1 (3) ° from precession photography and diffractometer measurements. Z=2, M=266.34, U=694.7 A 3, Dm (flotation)= 1.27, Dc= 1.273 g cm -3. The structure, refined to R= 0.069, consists of discrete molecules of nearly C2v symmetry and * Present address: Food Industries Ltd, Bromborough Port, Cheshire, England. the ethylene bridge is eclipsed with a torsional angle of 2.0 (6) ° .Introduction. The crystals were irregular prisms and data were collected for layers Okl to 6kl with a HilgerWatts linear diffractometer (Mo Ka radiation). 2947 reflexions were collected of which 1271 had intensities greater than 3tr. Lorentz and polarization corrections were applied (but none for absorption) and the layer scales were obtained from a Wilson plot. These were