Anomeric Effects in Sulfonyl Compounds: An Experimental and Computational Study of Fluorosulfonyl Azide, FSO₂N₃, and Trifluoromethylsulfonyl Azide, CF₃SO₂N₃

Fluorosulfonyl azide, FSO2N3, was characterized by IR (gas phase, Ar matrix), and Raman (liquid) spectroscopy. According to the matrix IR spectrum of 18O-labeled FSO2N3, its two oxygen atoms are nonequivalent. This assumption was confirmed by the X-ray crystal structure of FSO2N3 at −123 °C, as only one conformer was observed with one of the SO bonds in synperiplanar position to the N3 group (ϕ(OS−NN) = −14.8(3)°) with respect to the S−N bond. The same conformation was found for trifluoromethylsulfonyl azide, CF3SO2N3 (ϕ(OS−NN) = −23.74(15)°), in the solid state. The preference of such a synperiplanar configuration between SO and N3 was rationalized by a predominant anomeric interaction of nσ(N) → σ*(S−O), as supported by the experiment and quantum chemical calculations.