Conformational analysis—XXI : H NMR Conformational Study of Alkyl-Substituted 2-Oxo-1,3,2-Dioxathianes

2-Oxo-1,3,2-dioxathiane and all methyl- and several alkyl-substituted 2-oxo-1,3,2-dioxathianes were prepared for a ¹H NMR conformational study. The conformational energy of the axial SO group in CCl₄, - ΔG^θ_SO = 14.8±0.3kJ mol^?1, was determined by chemical equilibration of the epimeric cis-4,6-dimethyl derivatives and it was found to decrease with the increasing solvent polarity. The conformational equilibria of alkyl-substituted derivatives were solved and the proportions of the conformers estimated using ¹H NMR chemical shifts, vicinal coupling constants and in three cases also dipole moments. The configurational interactions in the C₄C₅C₆ moiety are close to the corresponding values of 1,3-dioxanes.