The investigation of the rotational spectra of fluoroformyliminosulfur difluoride, SF2NCOF, and pentafluorosulfanyliminosulfur difluoride, SF2NSF5 , was undertaken to determine, from the experimental moments Q.f inertia, the number and type of positional isomers and the bonding parameters. SF2NCOF and SF2NSF5 are the first iminosulfur difluorides (RN=SF2) to be investigated by microwave spectroscopy. The iminosulfur difluorides are characterized by a nitrogen-sulfur double bond with nonbonding pairs of electrons in an sp2 hybridized orbital on the nitrogen atom and in an sp3 hybridized orbital on the sulfur atom. This bonding scheme is expected to impart a unique charge distribution in the vicinity of the SF2 fluorines. In SF2NCOF the nitrogen-carbon bond may acquire some partial double bond character which can be described through resonance involving the S, N, C, and 0 atoms. The extent of this resonance would be expected to affect the length of the NC bond and to influence the height of the barrier to rotation about this bond.

For SF2NCOF and SF2NSF51 the question of cis-trans conformation about the nitrogen-sulfur double bond will be considered. Additionally, several rotameric forms of SF2NCOF which can arise from rotation about the nitrogen-carbon axis and which cannot be definitely precluded by presumptive reasoning will also be examined.