Calorimetric and computational study of 1,3-and 1,4-oxathiane sulfones

Article abstract of DOI:10.1021/jo0618472

(Chemical Equation Presented) The enthalpies of formation in the condensed and gas states, Δ_fH°_m(cd) and Δ_fH°_m(g), of 1,3- and 1,4-oxathiane sulfones were derived from their respective enthalpies of combustion in oxygen, measured by a rotating bomb calorimeter and the variation of vapor pressures with temperatures determined by the Knudsen effusion technique. Standard ab initio molecular orbital calculations at the G2(MP2) and G3 levels were performed, and a theoretical study on molecular and electronic structure of the compounds has been carried out. Calculated Δ_fH°_m(g) values at the G3 level using atomization reactions agree well with the experimental ones. These experimental and theoretical studies support that the destabilization found in 1,3-oxathiane sulfone, 11.2 kJ mol^-1 respecting to 1,4-oxathiane sulfone, is due to the electrostatic repulsion between the negative charges of the axial oxygen of the sulfone and the oxygen of the ring and apparently masks any stabilization originating from the hyperconjugative n_O → σ*_C-SO2 stereoelectronic interaction.