Vibrational analyses of sulfamoyl halides NH₂SO₂X (X is F, Cl and Br)

The structural stability of sulfamoyl halides NH₂-SO₂X (X is F, Cl and Br) were investigated by DFT-B3LYP/6-311 + G** and ab initio MP2/6-311 + G** calculations. From the calculations the molecules were predicted to exist only in the anti (X{single bond}S bond is anti with respect to nitrogen lone pair) conformation with the possibility of very low abundance of the syn (SO₂ and NH₂ groups eclipse each other) form of only the fluoride. The equilibrium constant for the syn ⇔ anti conformational conversion of sulfamoyl fluoride was calculated to be 0.0172 that corresponds to an equilibrium mixture of about 2% syn and 98% anti at 298.15 K. The vibrational frequencies were computed at DFT-B3LYP level for the stable anti conformer of the d₀ and d₂ (ND₂-SO₂X) deuterated species of the three molecules. Normal coordinate calculations were then carried out and the potential energy distributions were calculated for the molecules.