S-33 AND O-17 NUCLEAR-MAGNETIC-RESONANCE STUDIES OF AQUEOUS METHANESULFONIC AND TRIFLUOROMETHANESULFONIC ACIDS

The 33S and 17O NMR linewidths of trifluoromethanesulfonic acid (TFMSA) and methanesulfonic acid (MSA) decrease at lower concentrations in aqueous solution. Plots of 33S and 17O relaxation times vs MSA concentration are linear between 8 and 0.2 M. Relaxation times at infinite dilution and the effects of temperature and decoupling are reported for MSA. Decreased concentration dependence above 8 M appears to be related to decreased ionization and substantial solvation changes. For TFMSA, a similar break is observed for 33S relaxation above 5 M but 17O relaxation was entirely linear. For MSA, relaxation times of both nuclei are linearly correlated with the degree of ionization. For both anions, the 33S chemical shifts are concentration independent, but downfield 17O shifts are observed at lower concentrations. © 1991.