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 (XS 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.