orthonym.rules.ring_hydrogen#

Note

Internal API. Names and behaviour may change between releases.

Indicated and added hydrogen of a ring system whose atoms carry a double bond to an atom outside the ring (a ketone, thione or imine suffix, or an oxo, imino or ylidene prefix).

One rule for every producer that writes a fused or Hantzsch-Widman parent with such a group. The hydrogen of the name is that of the MANCUDE PARENT of the ring skeleton, with the groups accommodated afterwards:

  • (the Blue Book) “After the maximum number of noncumulative double bonds has been assigned to the ring structure, any ring atom with a bonding number of three or higher connected to adjacent ring atoms by single bonds only, and carrying one or more hydrogen atoms, is designated by indicated hydrogen”; (:14569) the same for fused systems.

  • (:3721) “in a preferred IUPAC name a locant and the symbol ‘H’ must be cited”;

    (:14607) “In preferred IUPAC names, all indicated hydrogen atoms must be cited”.

  • (:24766) “Indicated hydrogen is cited at any position of a ring system in order to accommodate principal characteristic groups… provided that there are an equal or greater number of indicated hydrogen atoms available”; (:24768) the indicated hydrogen atoms “are placed at peripheral atoms that will accommodate these principal characteristic groups” (‘7H-1-benzopyran-7-one (PIN)’:24776, ‘2H,7H-pyrano[2,3-b]pyran-2,7-dione (PIN)’ :24782); (:24794) the others go “to the lowest nonfusion peripheral atom”;

    (:24806) when there are fewer.

  • (:3725), (:24689) ‘added indicated hydrogen’ for the groups no indicated hydrogen accommodates, “cited in parentheses after the locant of the structural feature”, “preferred over the use of nondetachable hydro prefixes”; (:24721) none for a pair of groups that “simply removes a double bond”.

  • (:28410) “Ketones derived from mancude parent hydrides having indicated hydrogen atoms are named by direct substitution of a >CH2 group… When no indicated hydrogen is present, the methodology of ‘added indicated hydrogen’ is applied”: ‘4H-pyran-4-one (PIN) pyran-4-one’ (:28414), ‘1H-inden-1-one (PIN) inden-1-one’ (:28416), ‘naphthalen-1(2H)-one (PIN)’ (:28418).

  • Note (:24691): indicated hydrogen placed after the group is introduced (so that no added hydrogen is needed) “is not recommended for use in constructing IUPAC names”.

The placement itself is the bridged fused builder’s (bridged_fused_pin.hydro: hydro_state reads the mancude parent as a maximum matching over the atoms that keep a free valence after their ring bonds – so a neutral ring nitrogen with three ring bonds, which can carry neither kind of hydrogen, is never a position – and accommodate applies -.4 and /.3). A ring system without bridges is the same computation with no bridge atoms.

class orthonym.rules.ring_hydrogen.RingHydrogen(indicated, added, hydro, groups, state=None)#

Bases: object

Where the name of one ring system puts its hydrogen, as ring atom indices.

indicated: FrozenSet[int]#
added: FrozenSet[int]#
hydro: FrozenSet[int]#
groups: FrozenSet[int]#
state: Any = None#
orthonym.rules.ring_hydrogen.exocyclic_double_atoms(mol, ring_atoms)#

Ring atoms with a double bond to an atom outside ring_atoms (=O, =S, =NH, =CH2…), read from a Kekule form (an aromatic-flagged C=O ring carbon counts).

orthonym.rules.ring_hydrogen.ring_hydrogen(mol, ring_atoms, suffix_atoms, atom_to_locant)#

The indicated, added and hydro positions of ring system ring_atoms under the numbering atom_to_locant, with the =X groups of suffix_atoms expressed as suffixes (the other =X atoms of the system are prefixes, (:24864) “After the introduction of indicated and ‘added indicated hydrogen’ atoms, all substituent groups not expressed as suffixes are cited as prefixes”, so they are ordinary saturated positions here). None when the rule cannot be applied (a charged or radical ring atom, a parent with more than three indicated hydrogen atoms, a structure that is no hydro derivative of the mancude parent).

orthonym.rules.ring_hydrogen.indicated_text(rh, atom_to_locant)#

‘’ or ‘6H’ or ‘2H,5H’.

orthonym.rules.ring_hydrogen.added_text(rh, atom_to_locant)#

‘’ or ‘3H’ or ‘1H,5H’ (the text inside the parentheses after the suffix locants).

orthonym.rules.ring_hydrogen.hydro_text(rh, atom_to_locant)#

‘’ or ‘7,8-dihydro’ (None: a count with no multiplying prefix). (:16880): “If indicated hydrogen atoms are present in a name, the ‘hydro’ prefixes precede them”.

orthonym.rules.ring_hydrogen.parent_prefix(rh, atom_to_locant)#

The text written in front of the parent stem: ‘7,8-dihydro-2H,5H-’, ‘6H-‘, ‘3,4-dihydro’, ‘’ (None when the hydro count has no multiplying prefix). A hyphen ends the text when the stem must follow a locant (‘2H-’ + ‘pyran’); a bare hydro prefix joins a stem that starts with a letter directly (‘3,4-dihydro’ + ‘quinolin…’), the caller adds the hyphen before a stem that starts with a locant or a bracket.

orthonym.rules.ring_hydrogen.numbering_key(rh, atom_to_locant, suffix_atoms)#

(:25036-25044) (c) indicated hydrogen, (d) principal group as suffix, (e) added indicated hydrogen, (f) hydro prefixes: the part of the lowest-locants comparison this rule decides (the producer appends its prefix locants, (g)).