Chemistry of the phenoxathiins and isosterically related heterocycles. XXX . The crystal and molecular structure of 2‐AZA‐phenoxathiin 2‐oxide: Further evidence in support of the relationship between the 13 C‐NMR chemical shift of C‐10a resonance and the molecular dihedral angle

The synthesis of 2‐azaphenoxathiin 2‐oxide ( 4 ) and the total assignment of the 13 C‐nmr spectrum is described. Facile assignment was obtained from the assigned spectrum of 2‐azaphenoxathiin with additivities obtained from a comparison of 1‐azaphenoxathiin and its N ‐oxide. The crystal structure has also been determined from three dimensional X‐ray diffraction data. The compound crystallizes in the monoclinic space group P2 1 /n with a = 17.50(2)Å, b = 7.147(3)Å, c = 16.044(7)Å, β = 110.60(5) and Z = 8. Intensity data were collected at ‐ 135 ± 2°C on an automatic diffractometer using nickel‐filtered CuKα radiation. The structure was solved by direct methods and was refined by least‐squares techniques to give a final R‐value of 0.045 for all 3831 independent reflections.