Structural stability, S–O rotational barrier and vibrational analyses of monomeric non-planar halosulfonic acids X–SO2–OH (X = F, Cl and Br)

The structural stability of halosulfonic acids X–SO2–OH (X = F, Cl and Br) were investigated by DFT-B3LYP/6-311+G** and ab initio MP2/6-311+G** calculations. The potential energy curve for the XSOH internal rotation around S–O bond was consistent with one minimum that corresponds to non-linear structure with XSOH torsional angle of about 80°. The vibrational frequencies were computed at DFT-B3LYP level for the stable non-planar structure of the three molecules. Normal coordinate calculations were then carried out and the potential energy distributions (PED) were calculated for the molecules. On the basis of PED values and comparison with experimental data reliable assignments were provided for normal modes of fluoro-, chloro- and bromosulfonic acids.