(Fluorocarbonyl) sulfenyl isocyanate, FC(O)SNCO: unusual conformational properties

The geometric structure of (fluorocarbonyl)sulfenyl isocyanate, FC(O)SNCO, was determined by gas electron diffraction. Only a syn-syn conformation (carbonyl CO syn with respect to SN and the NCO group syn to CS) is compatible with the experimental diffraction intensities. This structure possesses an extremely short contact between the carbonyl oxygen atom and the isocyanate carbon atom of 2.65 Å as compared to the van der Waals distance of 3.20 Å. Several theoretical calculations (ab initio and density functional methods) confirm that this conformer represents the most stable structure.