STRUCTURAL STUDY OF FLOBUFEN .2. AN UNEXPECTED ROLE OF PACKING EFFECTS ON THE DIHEDRAL ANGLE OF PHENYL RINGS IN CRYSTAL-STRUCTURES OF 2,4-DIFLUOROBIPHENYLS

The absolute structure of the (R)-(+)-1-phenylethylammonium salt of (R )-(+)-flobufen (4-(2',4'-difluorobiphenyl-4-yl) -2-methyl-4-oxobutanoi c acid) was determined by a single-crystal X-ray study. Comparison of the structure of this flobufen salt with those of flobufen and dehydro flobufen 4'-difluorobiphenyl-4-yl)-2-methylen-4-oxobutanoic acid) reve aled an unexpected coplanar arrangement of the 2,4-difluorobiphenyl gr oup in the flobufen salt. This effect was attributed to the predominan t role of the three-dimensional hydrogen-bond network of the molecular packing. (C) 1997 Elsevier Science S.A.