Abstract The results of a 13 C NMR spectral investigation involving 5, 6-dihydro-1, 4- oxathiins, 1, 4-tetrahydro [9, 10] benzoxathiin, trans-tetrahydro-1, 4-benzoxathiin, and the corresponding sulfoxides and sulfones are reported. An interpretation involving a dipolar structure with (2p [RIGHTWARDS ARROW] 2p) π conjugation as opposed to (2p [RIGHTWARDS ARROW] 3d) π interactions with the vinyloxy sulfides seems consistent ...