Octaflurodibenzothiophen is synthesized by Ullmann coupling of bis (o- bromotetrafluorophenyl) sulphide and is shown to udergo nucleophilic substitution in the 2- position by methoxide ion. Similarly, substitution in octafluorothianthren occurs in the 2- position. The orientation of substitution in octafluorodibenzothiophen was deduced from the NMR spectra of the products and of the biphenyls which are produced by desulphurization ...