2 CONFORMATIONAL ISOMERS OF 2,3-(BIBENZYL-2,2'-DIYL)METHANO-1,4-NAPHTHOQUINONE

The crystal structures of the two conformational isomers of the title compound, rahydro-1H'-cyclopropa[b]naphthalene-2',7'-dione], C25H17BrO 2, have been determined by X-ray diffraction. Isomer (I) has a conform ation in which the spirodibenzocycloheptane moiety is close to the Br atom with a distance of 2.96 (3) Angstrom between the Br atom and the H atom at the 4-position of the tricyclic system. Isomer (II), obtaine d on heating (I), has a conformation in which the cycloheptane ring is flipped over apart from the Br atom and is characterized by the signi ficantly short bibenzyl ethylene bond [1.458 (11) Angstrom].