An unambiguous synthesis of heptafluoro-2-methoxydibenzothiophen (7) is reported. Structures for the products of substitution by MeO− in octafluorodibenzothiophen (1), octafluorofluoren-9-one (3), and the related octafluoro-2,2′-dihydrobiphenyl (4) and 19F NMR assignments are amended. Orientation of nucleophilic substitution in 2,2′-dibromooctafluorobiphenyl is established. The results of competition