orthonym.rules.lambda_convention

Note

Internal API. Names and behaviour may change between releases.

Shared λ-convention (lambda) infrastructure — IUPAC / Table 2.8.

The λ-convention cites the non-standard bonding number of a skeletal atom immediately after its locant, e.g. a tetravalent ring sulfur at locant 4 -> 4lambda4-thia (4lambda4-thiaspiro[3.5]nonane), or a hexavalent sulfur mononuclear hydride -> hexafluoro-lambda6-sulfane (SF6).

This module is the single source of truth for the standard-bonding-number table and the “is this valence non-standard?” decision. It was promoted verbatim from rules/spiro.py so that the spiro numberer, the acyclic skeletal-replacement namer, and the mononuclear-hydride / chalcogen / halogen namers all share one fail-closed implementation rather than each re-deriving Table 2.8.

References

IUPAC 2013 Blue Book, /3 (standard / nonstandard bonding number) IUPAC 2013 Blue Book, (λ placement: after the locant, no hyphen) IUPAC 2013 Blue Book, Table 1.5 (standard bonding numbers) [BBv2:6436] IUPAC 2013 Blue Book, (λ in chains / replacement nomenclature) IUPAC 2013 Blue Book, / (mononuclear hydrides bearing λ)

Fail-closed contract: a λ is emitted ONLY for a neutral atom present in STANDARD_BONDING_NUMBER whose actual valence differs from its standard value. Charged atoms and elements absent from the table are treated as standard (no spurious λ — never invent a descriptor the namer cannot justify).

orthonym.rules.lambda_convention.nonstandard_bonding_number(mol, atom_idx)

Return the lambda bonding number for a skeletal atom whose valence is non-standard, or None when the valence is standard.

The bonding number is the total count of skeletal/H bonds (RDKit GetTotalValence). It is emitted as lambda<n> immediately after the atom’s locant in the ‘a’-replacement prefix, e.g. a tetravalent ring sulfur at locant 4 -> 4lambda4-thia spiro example 4lambda4-thiaspiro[3.5]nonane), or on a mononuclear hydride parent (no locant) -> hexafluoro-lambda6-sulfane (SF6, /.

Fail-closed: only neutral atoms present in STANDARD_BONDING_NUMBER can carry a lambda; charged/exotic atoms return None (no spurious lambda).

orthonym.rules.lambda_convention.format_lambda_token(locant, lam)

Format a locant (+ optional lambda) into the citation token.

format_lambda_token(4, 4) -> "4λ4": the lambda follows the locant with no separator); format_lambda_token(4, None) -> "4". Shared by the spiro numberer and the acyclic skeletal-replacement namer so the on-the-wire spelling is identical everywhere.