On the experimental measurement of barriers to four-fold internal rotation in pentafluorosulfanyl-containing compounds: The microwave spectra of C₃H₅-SF₅ and C₄H₇-SF₅

Propen-1-yl sulfur pentafluoride, when examined using very high resolution spectroscopy, displays spectral effects arising from the presence of an unusual fourfold internal rotation. These observations have been recorded and anaylzed to produce a barrier height to the motion, V₄ = 260.8 cm⁻¹. No such spectral effects were resolved for either of the two lowest energy conformers of but-1-enyl sulfur pentafluoride which is consistent with a higher barrier to internal rotation for those species. These measurements allow the first considerations regarding how the shape and size of the molecular frame can hinder this type of internal motion.