Vibrational spectroscopic and theoretical calculation studies on conformational behavior of simple sodium 1-alkanesulfonates

Abstract The conformational behavior of sodium 1-propanesulfonate and sodium 1-butanesulfonate has been studied in the solid state and in aqueous solution by Raman spectroscopy and theoretical calculations. For sodium 1-butanesulfonate, the molecules of the anhydride and the hydrate crystallize in two different conformations. The characteristic C–S stretching bands were observed at 790–805 cm −1 for the trans (T) conformation around the CC–CS bond and at 728–766 cm −1 for the gauche ± (G ± ) conformation. The enthalpy difference between the G ± and T conformers of 1-propanesulfonate ion, H G ± − H T , was obtained as 4.3±0.4 kJ mol −1 in aqueous solution, while the energy difference between these conformations was calculated as 3.07, −0.41 and 0.02 kJ mol −1 by the HF, MP2 and B3LYP methods, respectively, using the 6-31G ∗∗ basis set. The inconsistency of the conformational stability between the experimental and theoretical results was discussed. The relationship between the isolated C–D stretching wavenumbers and the conformations around the CC–C(D)–CSO 3 − bonds is used to determine the local conformation.