Synthesis and carbon‐13 nuclear magnetic resonance spectroscopy of 5,6‐dihydro‐2‐methyl‐1,4‐oxathiin, trans ‐tetrahydro‐1,4‐benzoxathiin, 1,4‐tetrahydro‐[9,10]benzoxathiin, the 4‐oxides, 4,4‐dioxides and related acyclic compounds

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 (2 p →2 p )π conjugation as opposed to (2 p →3 d )π interactions with the vinyloxy sulfides seems consistent with trends in the 13 C NMR shifts. For the sulfoxides and sulfones, the substitutent‐induced chemical shift (SCS) effects at the β vinylic carbons (βSO and βSO 2 effects) are considerably less than those at sp 3 carbons. The γSO and γSO 2 values at the sp 2 γ carbons indicate deshielding , in contrast to the shielding at the sp 3 carbons.