orthonym.rules.azolium_cations

Note

Internal API. Names and behaviour may change between releases.

Names of ring cations of the azolium kind: the added hydron and the indicated hydrogen of the parent hydride sit on two ring nitrogens, the Blue Book), and the substituents replace the hydrogens. The producers of ions._emit_ring_cumulative_suffix name a ring cation from the numbering of its neutral ring, which cannot place the indicated hydrogen and the ‘-ium’ on different nitrogens when both carry a substituent, or when both are protonated.

orthonym.rules.azolium_cations.azolium_hydron_centres(mol, ring_system, center_idx)

The ring nitrogens at which the charge of the azolium mol can be drawn, center_idx first: an aromatic ring N bearing an exocyclic substituent and no hydrogen, with the positive charge on it in a resonance structure of mol and none elsewhere. In 1,3-dimethylimidazolium both nitrogens are such centres; the cation is one species and the name cannot depend on which nitrogen the drawing charges.

orthonym.rules.azolium_cations.azolium_demote_name(mol, ring_system, center_idx)

(heading the Blue Book): “A cation derived formally by adding one or more hydrons to any position of a neutral parent hydride… is named by replacing the final letter ‘e’ of the parent hydride name, if any, by the suffix ‘ium’”; “1H-imidazol-3-ium (PIN)” (:41396). An azolium whose ring nitrogens all carry a substituent (1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1,3-dimethylbenzimidazolium) is that cation with the substituents replacing the hydrogens: the indicated hydrogen of the parent hydride and the added hydron sit on the two nitrogens, and a substituent stands on each.

The parent hydride is the ring with every substituent replaced by hydrogen, one nitrogen bearing the indicated hydrogen (_bare_parent); its own numbering puts that hydrogen at the lowest locant, (heading:3219) criterion (b) “indicated hydrogen for unsubstituted compounds” (:3246), and the ‘-ium’ takes the other nitrogen, criterion (c) “principal characteristic groups and free valences (suffixes)” (:3256). Which nitrogen is the indicated-hydrogen position is left open by the structure, so each nitrogen that can carry the charge is tried and the cation is named once, by the choice the rules leave: the locant set of the prefixes (f) “detachable alphabetized prefixes, all considered together in a series of increasing numerical order” (:3301), then (g) “lowest locants for the substituent cited first as a prefix in the name” (:3307; ‘1-methyl-4-nitronaphthalene (PIN)’,:3318). The drawing therefore does not change the name. Every candidate is read back by OPSIN with the hydron on the same atoms (_cation_name_rt_ok); ‘’ (decline) when none is, or the ring is not an azolium of this kind.

orthonym.rules.azolium_cations.azolium_hydron_site_name(mol, ring_system, cation_idx)

The azolium whose added hydron sits on cation_idx ([nH+]) and whose other ring nitrogen carries the substituent (Nc1c[nH+]cn1C): (heading the Blue Book),:41368, “A cation derived formally by adding one or more hydrons to any position of a neutral parent hydride”, PIN ‘1H-imidazol-3-ium’ (:41396), the substituents replacing hydrogens, so the substituted nitrogen is the indicated-hydrogen position of the parent hydride. (:42219): “This is consistent with the choice of lowest locants for corresponding neutral compounds (see “; with (b) the indicated hydrogen (:3246) and (c) the ‘ium’ (:3256) at 1 and 3 in both numberings, (f) (:3301) “detachable alphabetized prefixes, all considered together in a series of increasing numerical order” gives ‘5-amino-1-methyl-1H-imidazol-3-ium’ ({1,5}), not ‘4-amino-3-methyl-’ ({3,4}). The producers of ions decline a ring that carries a principal group (amino, carboxy, hydroxy, cyano…) as a suffix, so this drawing had no name and the form choice shipped the other drawing’s, with the ‘ium’ on the substituted nitrogen (decision LO9). Read back by OPSIN with the hydron on the same atom (_cation_name_rt_ok); ‘’ (decline) for another ring, a second ring NH or substituted nitrogen, or any other charge.

orthonym.rules.azolium_cations.azolium_zwitterion_name(mol, ring_system, cation_idx, anchor)

The zwitterion of an azolium whose added hydron sits on cation_idx ([nH+]), whose indicated-hydrogen nitrogen carries a substituent, and whose ring carries a carboxylate (anchor = (carboxyl carbon, ring atom it hangs on)), in one numbering: “Zwitterionic compounds with at least one ionic center on a characteristic group” (the Blue Book),:42447, cationic suffix before anionic, “ionic centers on skeletal atoms of the parent hydride are preferred to the locants for positions of attachment of characteristic groups denoted by ionic suffixes”, over the parent hydride of (:41368, ‘1H-imidazol-3-ium (PIN)’,:41396): Cn1cc(C(=O)[O-])[nH+]c1C is ‘1,2-dimethyl-1H-imidazol-3-ium-4-carboxylate’. The parent is the ring with every substituent replaced by hydrogen (_bare_parent), so the substituted nitrogen is its indicated-hydrogen atom (b),:3246) and the numbering of the parent, which ranks the ‘ium’ (c) and then the carboxylate, is the one the prefixes are cited in. A ring that is not a five-membered monocycle with that one substituted nitrogen, or whose stem cites an indicated hydrogen elsewhere than the nitrogen the numbering gives it, is declined (‘’).

orthonym.rules.azolium_cations.ring_has_other_nh_heteroatom(mol, ring_system, center_idx)

True if a ring heteroatom other than center_idx carries hydrogen (the NH of a benzimidazolium or a triazolium drawn with both nitrogens protonated). The neutral parent then cites an indicated hydrogen (‘1H-‘), a position of its own numbering, and the ‘-ium’ is cited at the centre’s locant read from the numbering of the neutral ring, which does not know which of two equivalent nitrogens holds that hydrogen: the two locants can name one nitrogen twice (‘1H-1,3-benzimidazol-1-ium’, the NH2+ cation).