Revised Nomenclature for Radicals, Ions, Radical Ions and Related Species
(IUPAC Recommendations 1993)

RC-82.5. Multiple Cationic Centers

Continued from RC-82.3. Cationic heterocycles in which the cationic center results from skeletal bonding of a heteroatom

Contents of this section

RC-82.5. Cationic compounds with multiple cationic centers
- RC-82.5.1. Polycations with cationic centers identically derived at two or more positions on the same parent hydride
- RC-82.5.2. "Ium" and "ylium" centers in the same parent hydride
- RC-82.5.3. Polycations with cationic centers identically derived by the addition of one hydron to each of two or more of the characteristic groups given by Table 4 in RC-82.1.2.1
- RC-82.5.4. Cationic characteristic groups on parent cations
- RC-82.5.5. Assemblies of parent cations
- RC-82.5.6. Other polycations with cationic centers on characteristic groups
- RC-82.5.7. Polycations derived from diimides and polyimides
- RC-82.5.8. Cationic centers in both parent compounds and substituent groups
  - RC-82.5.8.1. Prefixes for expressing the mononuclear parent cations described by RC-82.1.1.1 as monovalent substituents
  - RC-82.5.8.2. Prefixes for expressing monocationic polynuclear parent hydrides with the free valence at a heteroatomic cationic center
  - RC-82.5.8.3. Systematically derived prefixes for expressing cationic structural units as substituents
  - RC-82.5.8.4. Choice of parent cationic structure

RC-82.5. Cationic compounds with multiple cationic centers.

RC-82.5.1. Polycations with cationic centers identically derived at two or more positions on the same parent hydride are named using appropriate numerical prefixes and operational suffixes as given in RC-82.1.1.2 and RC-82.2.2.2 or replacement prefixes as given in RC-82.4.

RC-82.5.2. "Ium" and "ylium" centers in the same parent hydride. Cationic compounds with two or more cationic centers in the same parent hydride structure, at least one being derived formally by the addition of a hydron to a skeletal position and at least one by the loss of a hydrogen atom as a hydride ion from another skeletal position, are named by replacing the final "e" of the parent hydride name by the operational suffix "-ium", followed by the operational suffix "-ylium", each preceded, where necessary, by appropriate numerical or multiplicative prefixes and locants (see RC-82.1.1.2 and RC-82.2.2.2).

Where there is a choice, low locants of the parent hydride are given first to the cationic centers regardless of their type, and then to "-ylium" cationic centers.

Examples:

	1-methyl-5H-cyclohepta[b]pyridin-1-ium-5-ylium 1-methyl-5H-1-azoniabenzocyclohepten-5-ylium
	4,4-dimethylpiperazin-4-ium-1-ylium

RC-82.5.3. Polycations with cationic centers identically derived by the addition of one hydron to each of two or more of the characteristic groups given by Table 4 in RC-82.1.2.1, except for imides (for which see RC-82.5.7) and acids, are named by using multiplicative prefixes, such as "bis-", and "tris" with the appropriate cationic suffix.

Dications and polycations so derived from diacids and polyacids are named by adding numerical prefixes, such as "di-" and "tri-", to the term "acidium".

Examples:

	N,N,N',N'-tetramethylethane-1,2-bis(aminium) N,N,N',N'-tetramethylethylenebis(aminium)
	hexanedioic diacidium

RC-82.5.4. Cationic characteristic groups on parent cations. Cationic compounds with cationic centers both in the parent hydride part of the structure and on a characteristic group expressible as a cationic suffix (see RC-82.1.2.1, RC-82.2.3.2, and RC-82.2.3.3) may be named by adding the cationic suffix to the name of a parent cation formed according to RC-82.1.1, RC-82.2.2, RC-82.3, RC-82.4, or RC-82.5.2.

Examples:

	N,N,N,1-tetramethylquinolin-1-ium-3-aminium
	5λ⁵-quinolizin-5-ylium-2-carboximidamidium (see footnote to Table 4 in RC-82.1.2.1)

Where there is a choice, low locants for skeletal cationic centers are determined before considering low locants for positions at which cationic suffixes are attached.

Example:

N,N,N,2-tetramethyl-2,6-naphthyridin-2-ium-5-aminium
(not N,N,N,6-tetramethyl-2,6-napthyridin-6-ium-1-aminium)

RC-82.5.5. Assemblies of parent cations. Cationic compounds with cationic centers identically derived from the same parent hydride but located in different parts of the structure are named, if possible, by the principles for naming assemblies of identical units (ref 2q) using the multiplicative prefixes "bis-", "tris-", etc., where necessary.

Note: The multiplicative prefixes "bis-", "tris-", etc. are used to avoid the possibility of confusion that could arise from the use of the numerical prefixes "di-", "tri-", etc.

Examples:

1,4-phenylenebis(phosphonium)

1,1'-dimethyl-4,4'-ethylenedipyridin-1-ium
(IUPAC multiplicative method; see RC-80.11)
4,4'-ethylenebis[1-methylpyridin-1-ium]
(CAS multiplicative method; see RC-80.11)

	1,1'-oxydicyclohepta-2,4,6-trien-1-ylium
	1,1',3,3'-tetramethyl-2,2'-oxybis(2,5-dihydro-1H-imidazol-3-ium) (IUPAC multiplicative method; see RC-80.11) 2,2'-oxybis[1,3-dimethyl-2,5-dihydro-1H-imidazole-3-ium] (CAS multiplicative method; see RC-80.11)
	2,2'-(1,3-phenylene)dipropan-2-ylium (see RC-82.2.2.2 and RC-80.8) 1,1'-dimethyl-1,1'-(1,3-phenylene)diethylium (see RC-82.2.2.1 and RC-80.8) (IUPAC multiplicative method; see RC-80.11) 1,1'-(1,3-phenylene)bis[1-methylethylium] (see (RC-82.2.2.1 and RC-80.8) (CAS multiplicative method; see RC-80.11)

RC-82.5.6. Other polycations with cationic centers on characteristic groups. Cationic compounds with two or more cationic centers identically derived from the same characteristic group, except for diimides and polyimides (for which see RC-82.5.7), diacids and polyacids (for which see RC-82.2.3.2 and RC-82.5.3), and the other characteristic groups given by Table 4 in RC-82.1.2.1, as described in RC-82.5.3, are named if possible on the basis of a cationic parent hydride according to the principles for naming assemblies of identical units (ref 2q) using the multiplicative prefixes "bis-", "tris-", etc., where necessary to avoid possible confusion that may arise from the use of the numerical prefixes "di-", "tri-", etc.

Note: Accordingly, cationic centers derived from two or more of the same characteristic group are not described in terms of that characteristic group using appropriate multiplicative prefixes.

Examples:

	pentane-2,4-diylidenebis(oxonium) (see RC-80.8) (1,3-dimethylpropan-1,3-diyl)bis(oxonium) (see RC-80.8)
	O,O'-dimethyl-O,O'-diphenyl[ethylenebis(oxonium)] (IUPAC multiplicative method; see RC-80.11) ethylenebis[methylphenyloxonium] (CAS multiplicative method; see RC-80.11)
	phthaloylbis(disulfanylium)
	ethylenebis(azanylium) ethylenebis(aminylium)
	butane-1,4-diylidenebis(azanylium) butane-1,4-diylidenebis(aminylium)
⁺O-CH₂-CH₂-O⁺	ethylenebis(oxidanylium)
	pyridine-2,6-diylbis(sulfanylium)
	benzene-1,4-disulfonylbis(dioxidanylium)
⁺O-S-SO₂-CH₂-CH₂-SO₂-S-O⁺	[ethane-1,2-disulfonylbis(sulfanediyl)]bis(oxidanylium)

RC-82.5.7. Polycations derived from diimides and polyimides by either addition of hydrons to, or removal of hydrogen atoms as hydride ions from, two or more nitrogen atoms of a diimide or polyimide are described on the basis of a heterocyclic parent cation name derived according to RC-82.1.1.2, RC-82.2.2.2, or RC-82.5.2.

Examples:

	2,2',5,5'-tetraoxo[3,3'-bipyrrolidine)-1,1'-diium
	1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydrobenzo[1,2-c;4,5-c']dipyrrole-2,6-bis(ylium) (RC-82.2.2.4) 1,3,5,7-tetraoxo-5,7-dihydrobenzo[1,2-c:4,5-c']di-pyrrole-2,6(1H,3H)-bis(ylium) (RC-82.2.2.4)
	1,3,6,8-tetraoxo-1,2,3,6,7,8-hexahydrobenzo[lmn][3,8]phenanthrolin-7-ium-2-ylium (RC-82.2.2.4) 1,3,6,8-tetraoxo-3,6,7,8-tetrahydrobenzo[lmn][3,8]phenanthrolin-7-ium-2(1H)-ylium (RC-82.2.2.4)

RC-82.5.8. Cationic centers in both parent compounds and substituent groups. A polycation in which all catonic centers cannot be included in a cationic parent hydride or parent compound (or when it may not be desirable to do so) is named by selecting part of the structure that contains most of the cationic centers as the cationic parent hydride or parent compound [see RC-82.5.8.4(a)] to be named by the principles of these recommendations. Parts of the structure containing other cationic centers are then expressed by prefixes formed as described in the following subsections.

RC-82.5.8.1. Prefixes for expressing the mononuclear parent cations described by RC-82.1.1.1 as monovalent substituents are formed by changing the "-onium" ending of the parent cation to "-onio", (ref 2nn).

Examples:

	ammonio
	selenonio
	trichlorophosphonio
	phenyliodonio

RC-82.5.8.2. Prefixes for expressing monocationic polynuclear parent hydrides with the free valence at a heteroatomic cationic center may be derived by changing the "-ium" ending of the parent cation to "-io" (ref 2pp). Locants may be omitted provided that there is no resulting ambiguity.

Examples:

	pyridinio
	triaz-2-en-1-io

RC-82.5.8.3. Systematically derived prefixes for expressing cationic structural units as substituents are formed by adding the operational suffixes "-yl", "-ylidene", "-diyl", etc., with appropriate locants, to the name of the parent cation derived according to RC-82.1.1, RC-82.2.2, RC-82.3, or RC-82.5.2, or by replacing the final "e", if present, of a cationic replacement name (see RC-82.4) by these operational suffixes.

Note 1: The operational suffix "-ylidene" is to be used only to describe the presence of a double bond between the substituting group and a parent hydride or parent substituent (see RC-80.5).
Note 2: This method is also applicable to the cationic prefix groups considered in RC-82.5.8.1 and RC-82.5.8.2.

Examples:

	ammoniumyl ammonio (RC-82.5.8.1)
	ethan-1-ium-1-yl
	2-methylpropan-2-ylium-1-yl
	1-methylpyridin-1-ium-3-yl
	1-methyl-1-azoniabicyclo[2.2.1]heptan-3-yl (RC-82.4) 1-methyl-1-azabicyclo[2.2.1]heptan-1-ium-3-yl (RC-82.1.1.2)
	diazyn-1-ium-1-yl (traditional name: diazonio)

Note: The traditional name "diazonio" describes both structures, and -N=N⁺, whereas the systematic name given here describes only the first of these structures; the name diazen-2-ylium-1-yl describes the second structure.

	methanyliumylidene
	dimethylazaniumylidene
	methylsulfaniumdiyl
	4-methylpyrazine-1,4-diium-1-yl

RC-82.5.8.4. Choice of parent cationic structure. Although, in theory, any portion of a polycationic structure that can be named by the principles in these recommendations can be the parent structure, it is often useful to have some guidelines for making this choice. Thus, when necessary or desirable, a parent cationic structure may be chosen by applying the following criteria in order until a definitive choice is achieved.

(a) the maximum number of cationic centers of any kind, including cationic suffix groups [This is in agreement with the principles for choosing a preferred component for naming fused heterocyclic ring systems (ref 3j)];
(b) the maximum number of "ylium" cationic centers;
(c) the maximum number of senior cationic centers, according to the nature of the cationic atom, in the same order as for the corresponding replacement prefixes (ref 3d, 11).

Further choice, if necessary, is made by applying the general criteria for chains and rings given in the 1979 IUPAC Organic Rules (ref 2cc).

Examples:

	dimethyl[6-(trimethylammonio)hexyl]sulfonium (RC-82.1.1.1, RC-82.5.8.1, and RC-80.8) 6-(dimethylsulfonio)-N,N,N-trimethylhexan-1-aminium (RC-82.1.2.1 and RC-82.5.8.1) 2,9,9-trimethyl-2-thionia-9-azoniadecane (RC-82.4)
	1-methyl-4-(trimethylphosphoniumyl)pyridin-1-ium (RC-82.5.8.3) 1-methyl-4-(trimethylphosphonio)pyridin-1-ium (RC-82.5.8.1)
	1,3-dimethyl-5-(methyloxoniumylidene)cyclohex-3-en-1-ylium
	2-[3-(trimethylammonio)phenyl]-1λ⁴-benzo[b]thiopyrylium (RC-82.5.8.1 and RC-82.3.2) 2-[3-(trimethylammoniumyl)phenyl]-1-benzothiopyrylium (ref 3h) (RC-82.5.8.3 and RC-82.3.2)
	2-(dimethyloxoniumyl)-5λ⁵-quinolizin-5-ylium (RC-82.3.1 and RC-82.5.8.3) 2-(dimethyloxonio)-5λ⁵-quinolizin-5-ylium (RC-82.3.1 and RC-82.5.8.1)

1,1'-bis[1-(dimethylamino)-3-(dimethylazaniumylidene)prop-1-en-2-yl][4,4'-bipyriine]-1,1'-diium (see RC-80.8)
1,1'-bis[2-(dimethylamino)-1-[(dimethylazaniumylidene)methyl]vinyl][4,4'-bipyridne]-1,1'-diium (see RC-80.8)

References for this section

1. International Union of Pure and Applied Chemistry. Organic Chemistry Division. Commission on Nomenclature of Organic Chemistry, Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F and H, 1979 ed., Pergamon Press, Oxford, 1979, 559 p.

2. Reference 1, Section C, pp. 79-322: [q] Rules C-72, p. 130-1; and C-73, p. 132; [cc] Subsections C-0.13, pp. 97-101; and C-0.14, pp. 101-5; [nn] Rules C-82.1, p. 134-5, Table V, p. 135; and C-816.3, p. 260; [pp] Rule C-82.1, p. 134-5, Table V, p. 135, footnote.

3. Reference 1, Section B, pp. 53-76: [d] Rule B-1.1, pp. 53-5, Table I, p. 53; [h] Rule B-3.5, pp. 67-8; [j] Rule B-3.1, pp. 64-5.

11. International Union of Pure and Applied Chemistry. Organic Chemistry Division. Commission on Nomenclature of Organic Chemistry, Revision of the Extended Hantzsch-Widman System of Nomenclature for Heteromonocycles, Recommendations 1982, Pure Appl. Chem. 55, 409-16, 1983.

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