Pentafluorobenzaldehyde has been converted into a range of derivatives by reactions involving the carbonyl group, viz., a pentafluorostilbene, a pentafluorocinnamic acid, an azine, an oxime, and a range of acetals. Other derivatives were made by reactions involving replacement of fluorine using dimethylamine, sodium hydrogen sulphide, sodium thiophenoxide, and sodium methoxide.

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2.3.4.5.6-Pentafluorobiphenyl has been brominated with a mixture of bromine and aluminium tribromide to give 4'-bromopentafluorobiphenyl (90%). nitrated with a fuming nitric-sulphuric acid mixture in glacial acetic acid to give 4'-nitro-and 2'-nitropentafluorobiphenyl in the ratio of 4 : 1, and methylated with a mixture of methyl bromide and aluminium tribromide to give a complex mixture containing mainly polymethylated pentafluorobiphenyls.THE bromination , nitration, and methylation of 2,3,4,5,6-pentafluorobiphenyl have been studied to determine its pattern of electrophilic substitution. This compound is known2 to be very susceptible to nucleophilic substitution and hence the degree of deactivation towards electrophilic attack was of particular interest.Pentafluorobiphenyl, bromine (1.1 mol.) , and aluminium tribromide in refluxing cyclohexane gave a solid in almost quantitative yield, based upon a bromopentafluorobiphenyl. This was shown by g.1.c. to contain four components, the proportions of which were estimated from their peak areas; pentafluorobiphenyl was found to comprise ca. 8% of the total product. The three other components were presumably the three isomeric bromopentafluorobiphenyls and the longest retained of them comprised ca., 0% of the total of these unidentified components.The major component had an elemental analysis consistent with it being a bromopentafluorobiphenyl and g.1.c. showed that it was a single compound. 1.r. spectroscopy indicated that it was the 4'-isomer and this was confirmed by the preparation of an authentic specimen from p-bromophenyl-lithium and hexafluorobenzene. In addition, this reaction gave some of a dibromo-tetrafluoroterphenyl, which from its mode of formation and high melting point was expected to have a para-orien t at ion .2The marked predominance of 4'-bromopentafluorobi-

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At 100 "C in toluene, cis-2'-trifluoromethylspiro [acenaphthene-1,7'-norcaradiene]-2-0ne (1 ; X = CF,) interconverts with its 3'-trifluoromethyl-~ubstituted isomer (2; X = CF,), this being the first directly observed example of a degenerate ring-walk rearrangement for a norcaradiene with a spiro-ring system attached a t C-7.