Conformational Studies by Dynamic NMR. 63.1 Stereodynamics of Dialkylamino Ethoxy Disulfides: S−S and S−N Rotation Processes

The title compounds (EtOS−SNR2) display diastereotopic OCH2 hydrogens below room-temperature owing to the existence of two stereolabile enantiomers brought about by the restricted S−S rotation in the adopted gauche conformer. A second dynamic process, which makes the N-bonded alkyl groups diastereotopic, was also observed at a much lower temperature (below −80 °C). On the basis of experimental observations and of ab initio calculations, the latter has been interpreted as due to the restricted rotation about the S−N bond. Line shape analysis of the variable temperature 1H and 13C NMR spectra allowed the free energies of activation to be determined for both motions in the case of R = Me, Et, Pri.