Sesquiterpenoids. Part VIII. Stereochemistry of santonin: X-ray analysis of 2-bromo-β-santonin

Crystals of 2-bromo-β-santonin are orthorhombic, of space group P212121, with four molecules of C15H17BrO3 in a unit cell of dimensions a= 7·50, b= 12·43, c= 15·41 A. The atomic co-ordinates were determined by Fourier and least-squares calculations, and the final value of R over 1389 independent reflexions is 8·4%. The bond lengths and valency angles do not differ significantly from those of 2-bromo-α-santonin, but the C(13)⋯ C(6) and C(13)⋯ C(8) intramolecular separations (3·17 and 3·07 A) are distinctly smaller than those in the α-isomer (3·79 and 3·49 A).