Molecular and vibrational structure of thiosulfonate S-esters

S-methyl methanethiosulfonate (1), S-ethyl ethanethiosulfonate (2), S-isopropyl propane-2-thiosulfonate (3), S-tert-butyl 2-methylpropane-2-thiosulfonate (4), and S-phenyl benzenethiosulfonate (5) were investigated by FTIR spectroscopy in liquid solution and by quantum chemical calculations (B3LYP/cc-pVTZ). The vibrational spectra of 2 and 3 are sensitive to the orientation of the alkyl group attached to the sulfonylic sulfur atom. Rotamers corresponding to anti and gauche conformations are thus predicted to have distinctly different vibrational transitions in the 800–400 cm−1 region. The observed vibrational spectra of 2 and 3 must be assigned to overlapping contributions from different rotamers, in agreement with the calculated transitions.