Fluorine-19 NMR spectroscopy of polyhalonaphthalenes. Part II polychloropolyfluoronaphthalenes via nucleophilic fluoride dechlorination

Six new polychloropolyfluoronaphthalenes have been identified by F-19 NMR whose empirical formulae are C₁₀ Cl_8−n F_n where n is 5 and 6 two trichloropentafluoronaphthalenes and four dichlorohexafluoronaphthalenes:-

• 1,3,8-trichloro-2,4,5,6,7-pentafluoronaphthalene,

• 1,3,6-trichloro-2,4,5,7,8-pentafluoronaphthalene,

• 1,3-dichloro-2,4,5,6,7,8-hexafluoronaphthalene,

• 1,8-dichloro-2,3,4,5,6,7-hexafluoronaphthalene,

• 1,6-dichloro-2,3,4,5,7,8-hexafluoronaphthalene and

• 2,7-dichloro-1,3,4,5,6,8-hexafluoronaphthalene.

In the partly fluorinated compounds such as 1,3,6,8-tetrachloro- 2,4,5,7-tetrafluoronaphthalene, nucleophilic fluoride dechlorination occurs at both and β positions. Initial substitution in octachloronaphthalene is more selective and occurs predominantly at the -position; both subsequent exchanges occur at sites two carbons away from the initial site. The results support the idea that the transition state is stabilised by chlorine at the sites of electron density, ortho and para to the site of nucleophilic attack.