The effects of fluorine and chlorine substituents across the fjords of bifluorenylidenes: Overcrowding and stereochemistry

Abstract

The bistricyclic aromatic enes (BAEs) (E)- and (Z)-1,1′- difluorobifluorenylidene, 1,8,1′,8′-tetrafluorobifluorenylidene, (E)-and (Z)-3,3′-difluorobifluorenylidene, 3,6,3′,6′- tetrafluorobifluorenylidene, and their chlorinated analogues were subjected to a DFT study of overcrowding in their fjord regions. The B3LYP hybrid functional was employed to calculate energies and geometries of the twisted conformations of these BAEs. The diastereomers E11′F2 and Z11′F2 have identical twist angles (ω = 37.1°) and similar degrees of overcrowding, but differ in the degree and mode of pyramidalization, χ. In E11′F2, χ(C9) = +χ(C9′) = 7.0° (syn-pyramidalization), while in Z11′F2, χ(C9) = -χ(C9′) = 1.0° (a..