13C and 17O chemical shifts and conformational analysis of mono‐ and di‐methyl‐substituted thiane 1‐oxide and thiane 1,1‐dioxide

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Abstract
The 13C and 17O (natural abundance) chemical shifts of several mono‐ and di‐methyl ring‐substituted thiane 1‐oxides and thiane 1,1‐dioxides are reported. The cis and trans isomers of methyl‐substituted thiane 1‐oxide are readily identified by 13C and 17O NMR. In particular, the 17O NMR signals of axial SO groups are found several ppm upfield of those of the equatorial counterparts. The proportion of axial and equatorial conformers of thiane 1‐oxide in different solvents has been measured by low‐temperature 13C NMR. In THF the proportion of the axial conformer is higher than in CD2Cl2 whereas in CDCl3 or CHF2Cl the conformational preference is reversed and the equatorial conformer is slightly favoured.