Hantzsch-Widman replacement: oxa = Z(O) = 8; thia = Z(S) = 16; aza = Z(N) = 7 (periodic-table classifier)

Layer 2 — Chemistryin the chemical-nomenclature subtree

Hantzsch-Widman prefix-to-atomic-number classifier: oxa → Z=8 (oxygen), thia → Z=16 (sulfur), aza → Z=7 (nitrogen). Canonical pins: three exact integers from the periodic table.

Related concepts

Hantzsch-Widman heteroatom-replacement framework: standard prefix table (oxa/thia/aza) for monocyclic heterocycles
Character orthogonality: (1/|G|)Σ χ_i(g) χ_j(g)* = δ_{ij}

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