Downfield chemical shifts at ?-protons and carbons of ?-propiothiolactones

Both the α-protons and carbons of β-propiothiolactones exhibit atypical downfield chemical shifts. The α-protons of β-propiothiolactones with no heteroatom at the α-position appear at 3.53–5.35 ppm, whereas the α-carbons appear at 56.9–86.2 ppm. The major cause of the unexpected deshielding effect was rationalized by assuming a through-space interaction between the occupied orbital of the α-carbon and the vacant orbital of sulfur.