The low-temperature 19F NMR spectra of (pentafluoropheny1)sulfur trifluoride are explained by the trigonal bipyramid structure (la) with the pentafluorophenyl ring in the basal plane and a relatively high barrier to rotation about the C-S bond. In the presence of a hydrogen fluoride scavenger, there is a high barrier to intramolecular rearrangement of the sulfur fluorines about the sulfur atom. The single basal fluorine couples strongly with one ortho fluorine and weakly with the other, but the two apical fluorines couple equally with both ortho fluorines. A six-bond coupling between S-F andp-F is found in (pentafluoropheny1)sulfur trifluoride and in (pentafluoropheny1)sulfinyl fluoride, but not in (pentafluorophenyl)sulfonyl fluoride.
(PENTAFLuoR0PHENYL)sulfur trifluoride has a collapsed 19F spectrum for the S-F region at room temperature in solvents such as CFCl,, diethyl ether and methylene chloride. On chilling to -SO" in trichlorofluoromethane, the S-F region is resolved into a doublet of triplets, Fa, centered at +71.9 ppm and a triplet split into doublets of doublets, F1,, centered at -52.8 ppm. This pattern corresponds to a trigonal bipyramid structure (la), with chemical shifts and JFaFb (71 Hz) similar to other RSF, c0mpounds.l (la) (1b)