Tuning the Anomeric Effect in Sulfamide with Superacids.

This study shows that the anomeric effect (negative hyperconjugation) that arises in sulfamide, as a result of the relatively short S-N bonds, can be tuned by the utilization of superacidic media. Sulfamide was reacted in binary superacidic systems XF/MF (M=As, Sb; X=H, D) and HF/BF . The colorless salts formed, [X NSO NX ] [MF ] and [H NSO NH ] [BF ] were characterized by low-temperature vibrational spectroscopy. In the case of [H NSO NH ] [BF ] , a single crystal X-ray diffraction study was performed. The salt crystallizes in the monoclinic space group P2 /c with four formula units per unit cell. An exclusive N,N'-diprotonation was observed in the superacidic system HF/SbF when using several equivalents of the Lewis acid. Low-temperature vibrational spectra as well as a single-crystal X-ray structure of [H NSO NH ] 2 [SbF ] ⋅2 HF are reported. The salt crystallizes in the orthorhombic space group Pna2 with four formula units per unit cell. Upon mono- or diprotonation of sulfamide, remarkable structural changes of the sulfur-nitrogen bond lengths were observed. Herein, these changes are discussed together with quantum chemical calculations.