Conformational Analysis of 5-Methyl-1,3-oxathiane

Abstract

Computer simulation of conformational transformations of 5-methyl-1,3-oxathiane at the DFT PBE/3ζ, RI-MP2/λ2, and HF/6-31++G(d,p) levels of theory has shown that the interconversion between the equatorial (global minimum) and axial chair conformers occurs along several independent pathways through five flexible forms. Nine transition states corresponding to different half-chair forms, as well as symmetrical and unsymmetrical boat conformers, have been localized on the potential energy surface. The free conformational energy of the methyl group has been estimated at 0.9–1.0 kcal/mol by comparison of the calculated and experimental vicinal coupling constants in the ¹H NMR spectra.