RC-82.2. Cationic centers derived formally by the loss of hydride ions

Contents of this section

• RC-82.2. Cationic compounds with cationic centers derived formally by the loss of hydride ions
  • RC-82.2.2. Cationic centers in parent hydrides
    • RC-82.2.2.1. Monocationic centers in saturated acyclic and monocyclic hydrocarbons and the mononuclear EH₄ parent hydrides of the carbon family
    • RC-82.2.2.2. Cationic centers in parent hydrides other than those described by RC-82.2.2.1
    • RC-82.2.2.3. Diazonium ions
    • RC-82.2.2.4. Nondetachable hydro prefixes vs. added (indicated) hydrogen
    • RC-82.2.2.5. A number of trivial and abbreviated names
  • RC-82.2.3. Cationic centers on characteristic groups
    • RC-82.2.3.1. Established or traditional names
    • RC-82.2.3.2. Acylium ions
    • RC-82.2.3.3. Monocationic centers on nitrogen atoms of amine, imine, amide, or imide characteristic groups
    • RC-82.2.3.4. Cationic centers on oxygen atoms of acid, peroxy acid, hydroxy, or hydroperoxy characteristic groups
    • RC-82.2.3.5. Cationic centers on sulfur atoms of thio acid, thiol, or dithiohydroperoxy characteristic groups
    • RC-82.2.3.6. Cationic centers on other characteristic groups

RC-82.2.1. Radicofunctional names. Cationic compounds that can be considered as being derived formally by the removal of electrons from the corresponding radical may be named by adding the class name "cation" as a separate word after the name of the radical (see RC-81). Polycations are indicated by adding the numerical prefixes "di-", "tri-", etc., as appropriate, to the class term.

Note: Although such names are useful for cations where all cationic centers are located in a single parent structure, the method cannot be extended to polycations where one or more of the cationic centers must be expressed in a substituent to a parent structure and is not very useful in naming salts where an anion is specified.

H3C+	methyl cation
[C6H5]+	phenyl cation
	acetyl cation
	benzenesulfonyl cation
	chloroazanyl cation (see RC-81.1.2, Note 3) chloroaminyl cation (see RC-81.1.2, Note 3)
HCO-O+	(formyloxyl) cation
	ethane-1,2-diyl dication
	cyclohexylidene dication

RC-82.2.2.1. Monocationic centers in saturated acyclic and monocyclic hydrocarbons and the mononuclear EH₄ parent hydrides of the carbon family. A cationic center derived formally by the removal of one hydrogen atom as a hydride ion from a terminal atom of a saturated unbranched acyclic hydrocarbon; from an atom of a saturated monocyclic hydrocarbon; or from any of the mononuclear parent hydrides, methane (CH₄), silane (SiH₄), germane (GeH₄), stannane (SnH₄), and plumbane (PbH₄) is named by replacing the "-ane" ending of the name of the parent hydride by "-ylium" (see also RC-81.1.1).

Examples:

H3C+	methylium carbenium
(C6H5)3Si+	triphenylsilylium
	dimethylgermylium
	propylium
	1-methylethylium propan-2-ylium (see RC-82.2.2.2 and RC-80.8) isopropylium (traditional name, see item 1, Appendix, List A)
	cyclobutylium

Note 1: This recommendation is consistent with the generalized principles for naming and numbering acyclic substituent prefixes as given in Section D of the 1979 IUPAC Organic Rules (ref 4c, 10f) rather than the principles of Section A (ref 10g) and the ACS silicon rules (ref 12a), where a principal chain must terminate at the free valence position (see also RC-80.8).

Note 2: Suffixes based on "-ylene", "-ylidene", and "-ylidyne", such as "-ylenium", or "-ylidenium", are not used for describing cationic centers.

Although suffixes such as "-diylium", "-triylium", etc., should be unambiguous in the context of this rule, a certain amount of ambiguity is clearly possible because of terminology in the 1979 IUPAC Organic Rules (ref 2dd) where this type of cation is defined as derived formally by "loss of an electron or electrons from a radical at the free valence position(s)". Taken literally, this definition could mean that an ending such as "-diylium" would describe a divalent radical in which only one free valence has lost an electron to form the cation, i.e., the suffix "-diyl" describing the diradical , and the suffix "-diylium" describing the radical cation .

Note 1: The systematic names phosphane and arsane (ref 4g, 6b) must be used for naming cations derived from the mononuclear parent hydrides PH₃ and AsH₃ according to this recommendation. because use of the traditional names phosphine and arsine (ref 4g, 6b) would lead to the names phosphinylium and arsinylium, which are the same names that would be generated according to RC-82.2.3.2 from the well established names phosphinyl (ref 12b) and arsinyl (ref 13b), the names for the acyl groups H₂P(O) - and H₂As(O)- derived from phosphinic and arsinic acids, respectively. Even though the names phosphinoyl and arsinoyl for these acyl groups are recommended in the 1979 IUPAC Organic Rules (ref 4h), ambiguity will still exist.

Note 2: The name "aminylium" for the parent cation H₂N⁺ used in the 1979 IUPAC Organic Rules (ref 2dd) is continued in these recommendations as an alternative to "azanylium", derived from the parent hydride name "azane" (ref 6b, 14), even though "amine" is not used as a parent hydride name for NH₃ herein (see also footnote to Table 2 in RC-80.9.1, Note 4 to RC-81.1.2, and Note 2 to RC-81.2.3.1).

Note 3: Although the name "amine" would be quite consistent with parent hydride names, such as phosphine and arsine, and is used as such by Beilstein, it is not used as a parent hydride name in these recommendations because it has also been added to the name of a radical to form the name of a parent compound (ref 15), for example butylamine. In these recommendations, the term "amine" is used only as a suffix to denote the attachment of the -NH₂ group to a parent hydride, for example, pyridin-2-amine.

Note 4: The names for the cations HO⁺ and HOO⁺ are hydroxylium (ref 6e) and hydroperoxylium (ref 2s, 2dd), respectively, but, in keeping with tradition are not used as parent cations in substitutive nomenclature. For the substituted cations, see RC-82.2.3.4.

Note 5: Although such cations could also be named by adding the suffix "-ium" (see RC-82.1.1.2) to the name of a parent hydride in which the at the cationic center is described in the parent hydride name by the λ-convention (see RC-81.1.3.3), the use of "-ylium" with the name for a parent hydride with the atom in the standard valency state is much preferred.

H2N+	azanylium aminylium nitrenium
C6H5-S+	phenylsulfanylium
(CH3)4P+	tetramethyl-λ5-phosphanylium (ref 16) tetramethylphosphoranylium (ref 2dd, 4p) tetramethylphosphonium (see RC-82.1.1.1)
	3-methyltriaz-1-en-1-ylium
	heptamethyltrisilan-2-ylium
	4-cyclopropyltetrasulfan-1-ylium
	cyclooct-3-en-1-ylium
	furan-2-ylium

1,2-bis(4-methoxyphenyl)-2-phenylethen-1-ylium

	bicyclo[2.2.1]heptan-2-ylium
	spiro[4.5]decan-8-ylium
	propane-1,3-bis(ylium) [propane-1,3-diyllum according the 1979 IUPAC Organic Rules (ref 2dd)]
	2,2-dimethyldiazane-1,1-bis(ylium) 2,2-dimethylhydrazine-1,1-bis(ylium) [traditional parent hydride name (ref 14)]
	propane-2,2-bis(ylium) 1-methylethane-1,1-bis(ylium) (see RC-82.2.2.1 and RC-80.8)
	cyclobut-3-ene-1,2-bis(ylium)
	propane-1,2,3-tris(ylium)

Examples:

	methanediazonium methyldiazenylium
	benzothiazole-2-diazonium benzothiazol-2-yldiazenylium
	2,4-dioxopentane-3-diazonium (2,4-dioxopentan-3-yl)diazenylium (see RC-80.8) (1-acetyl-2-oxopropyl)diazenylium (see RC-80.8)
	benzene-1,4-bis(diazonium) 1,4-phenylenebis(diazenylium)

In the first method (ref 2g) the "hydro" derivative is described by specifying the hydrogen atom of the dihydro pair that remains after the cationic center is created by citing an italic capital H(H) and the locant for the skeletal atom at which that hydrogen atom resides, both enclosed in a set of parentheses, and inserted into the name of the corresponding unsaturated parent hydride immediately after the locant for the cationic center.

Note: This procedure is exactly analogous to the use of "indicated hydrogen" to describe saturated ring positions that remain after the introduction of suffixes for principal characteristic groups, such as "-one", into the name of a parent ring or ring system that otherwise expresses the maximum number of noncumulative double bonds (ref 2g).

3,5-dimethyl-1,4-dihydropyridin-1-ylium 3,5-dimethylpyridin-1(4H)-ylium

RC-82.2.3. Cationic centers on characteristic groups. Although cationic centers derived formally by the loss of a hydrogen atom as a hydride ion from a characteristic group can be named on the basis of parent cations derived from parent hydrides as given in RC-82.2.2, it is often convenient and/or desirable to name a cation on the basis of a larger parent structure. Hence, the following recommendations for describing cationic centers located on some, but not all, of the characteristic groups of substitutive nomenclature are presented.

RC-82.2.3.1. Established or traditional names. Names describing certain cationic species related to characteristic groups are established in the literature. The names hydroxylium and hydroperoxylium for HO⁺ and HOO⁺, respectively, were mentioned in Note 4 to RC-82.2.2 2. Such cations may be considered to have been derived by the loss of an electron from the corresponding radical (ref 2s, 6c) and named according to method (b) of Rule C-83.1 in the 1979 IUPAC Organic Rules (ref 2dd) by replacing the "-yl" ending of the univalent radical name by "-ylium". The name nitrylium for O₂N⁺ was mentioned in the footnote to Table 3 in RC-82.1.1.1, and the name nitrosylium for ON⁺ follows directly. The name carboxylium for HO₂C⁺ has been proposed (ref 19). The method could be extended to the oxy halogen radicals, such as chloryl, but not to multivalent radicals, such as carbonyl or sulfonyl because of potential ambiguity (see also RC-81.2.1). Nevertheless, names such as hydroxysulfonylium and chlorosulfonylium for HO₃S⁺ and ClO₂S⁺, respectively, have been proposed (ref 19).

RC-82.2.3.2. Acylium ions, i.e., cations having at least one chalcogen atom or nitrogen atom bonded to the cationic center(s) by a formal double bond that can be considered as derived formally from an acid characteristic group (except peroxy acid groups) by the loss of all hydroxy groups as hydroxide ions are named by replacing the "-ic acid" ending of the name, except for acids named by the carboxylic acid suffix, with "-ylium" or, occasionally, "-oylium", according to the rules for naming the corresponding acid halides (ref 2x, 4n). The carboxylic acid suffix is changed to "carbonylium".

Note: The use of compound prefixes for expressing acyl substituents is not applied in these rules (ref 2h) (see RC-80.6)

	acetylium
	hexanethioylium
	cyclohexanecarbonylium
	ethenesulfonylium
	dimethylphosphinoylium
	methylphosphonoylium
	glutarylium pentanedioylium
	pyridine-2,6-dicarbonylium

Note: Trivial and semisystematic names preferred for naming organic compounds according to IUPAC recommendations are used in the first cited names for the examples below.

	ethanaminylium
	anilinylium benzenaminylium
	cyclohexaniminylium (ref 2z) cyclohexylideneaminylium (ref 2aa) (see Note 2 under RC-82.2.2.2)
	acetamidylium
	1H-pyrrole-2-carboxamidylium
	succinimidylium 2,5-dioxopyrrolidin-1-ylium (RC-82.2.2.2)
	naphthalene-1,8-dicarboximidylium 1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-1,2-ylium (RC-82.2.2.2 and RC-82.2.2.4) 1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-ylium (RC-82.2.2.2 and RC-82.2.2.4)

The contracted forms methoxylium, ethoxylium, propoxylium, butoxylium, phenoxylium, acetoxylium, and aminoxylium are retained.

Substituents to such compound parent cations are expressed by prefixes in the usual manner. Except for the contracted forms noted above, the compound parent cation is enclosed in parentheses.

Note 1: The term "peroxylium" is more consistent with terms like peroxo, peroxide, and peroxy, even though "dioxyl", and presumably therefore "dioxylium", is used in the 1979 IUPAC Organic Rules (ref 2t).

Note 2: The names hydroxylium and hydroperoxylium for the cations HO⁺ and HO-O⁺, respectively (see Note 4 to RC-82.2.2.2), are not used when the hydrogen atom has been substituted by another atom or group.

CH3-O+	methoxylium
(CH3)3C-O-O+	tert-butylperoxylium (see RC-80.8) (2-methylpropan-2-yl)peroxylium (see RC-80.8)
ClCH2-CO-O+	chloroacetoxylium
CH3-CS-O+	(thioacetyl)oxylium
(CH3)2N-O+	dimethylaminoxylium

Note: The contracted form thioacetoxylium is not used because it could be ambiguous. Compare with the second example under RC-82.2.3.5

furan-2-carboselenoyloxylium

Examples:

	(2,2-dichloroethyl)sulfanylium 2,2-dichloro(ethylthiylium) (by analogy with RC-82.2.3.4)
CH3CO-S+	acetylsulfanylium acetylthiylium (by analogy with RC-82.2.3.4)
C6H5-S-S+	phenyldisulfanylium phenylperthiylium (by analogy with RC-82.2.3.4)

Examples:

C6H5-Se-Se+	phenyldiselanylium
CH3-CH2-S-O+	(ethylsulfanyl)oxidanylium ethyl(sulfanyloxylium) (see RC-82.2.3.4)
	(2-naphthylmethoxy)sulfanylium
CH3-CH2-N2+	ethylazanebis(ylium)
C6H5-CO-N2+	benzoylazanebis(ylium)
	(1-hydroxyethylidene)azanylium (1-hydroxyethylidene)aminylium (1-hydroxyethylidene)nitrenium
	2-benzoyldiazan-1-ylium 2-benzoylhydrazin-1-ylium [traditional parent hydride name (reg 14)]
CH3-CH2-O-Te+	ethoxytellanylium

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: [f] Rule C-16.1, p. 108; [g] Rule C-315.1, p. 172; [h] Rule C-403.2, pp. 185, 188, Note, p. 188; and Rule C-631.1, pp. 230-1; [s] Rules C-218.1, p. 161; and C-81.1, pp. 133-4; [t] Rule C-81.1, pp. 133-4; [x] Rules C-403, pp. 185, 188; C-481, pp. 206-7; C-641.7, pp. 236-7; and C-642.4, pp. 240-1; [z] Rule C-815.3(a), pp. 258-9; [aa] Rule C-815.3(b), pp. 258-9; [dd] Rule C-83.1, pp. 137-9; [hh] Rule C-931.1, pp. 289-90.

4. Reference 1, Section D, pp. 323-471: [c] Rule D-4.14, p. 374-5, esp. footnote, p. 374; and Rule D-6.12, pp. 409-10, Note. p. 410; [g] Rule D-5.11, p. 384, footnote; [h] Rule D-5.66, pp. 403-4; [n] Rules D-5.66, pp. 403-4; and D-5.67, p. 404.

6. International Union of Pure and Applied Chemistry. Inorganic Chemistry Division. Commission on Nomenclature of Inorganic Chemistry, Nomenclature of Inorganic Chemistry, Recommendations 1990, G. J. Leigh, ed., Blackwell Scientific Publications, Oxford, England, 1990, 289 p. [b] Section I-7.2.2.1, pp. 83-5, Table 17.2; [c] Section I-8.4.2.2, p. 113; [e] Section I-8.2.4, p. 107.

10. Reference 1, Section A, pp. 5-52: [f] Rule A-4, p. 14, ** footnote; [g] Rules A-1.2, p. 5; A-2.25, pp. 6-7; A-3.5, p. 13; A-4.1, p. 14; and A-4.4, p. 15.

12. American Chemical Society, "Report of the ACS Nomenclature, Spelling and Pronunciation Committee for the First Half of 1952": [a] F. Organosilicon Compounds, Chem. Eng. News 30, 4517-22 (1952); [b] E. Organic Compounds Containing Phosphorus, ibid., 4515-22.

13. American Chemical Society, "Chemical Substance Index Names", Appendix IV in the 1987-1991 Chemical Abstracts Index Guide, Chemical Abstracts Service, Columbus, Ohio, 1992: [a] §125, p. 129I-130I; [b] §294, Illustrative List of Substituent Prefixes, pp. 236I-242I; [c] §187, p. 176I.

14. International Union of Pure and Applied Chemistry. Inorganic Chemistry Division. Commission on Nomenclature of Inorganic Chemistry, "Nomenclature of Inorganic Chemistry: II.2. The Nomenclature of Hydrides of Nitrogen and Derived Cations, Anions, and Ligands (Recommmendations 1981)" Pure Appl. Chem. 54, 2545-52 (1982), Rule II.2.1, p. 2546.

15. American Chemical Society, "The Naming and Indexing of Chemical Substances from Chemical Abstracts" [a reprint of the Introduction to the Subject Index of Volume 56 (January-June 1962) of Chemical Abstracts, Chemical Abstracts Service, Columbus, Ohio, 1962, §255-7, pp. 41N-42N.

16. International Union of Pure and Applied Chemistry. Organic Chemistry Division. Commission on Nomenclature of Organic Chemistry, Treatment of Variable Valence in Organic Nomenclature (Lambda Convention), Recommendations 1983, Pure Appl. Chem. 56, 769-78 (1984).

19. International Union of Pure and Applied Chemistry. Organic Chemistry Division. Commission on Physical Organic Chemistry, "Nomenclature for Organic Chemical Transformations, Recommendations 1988", Pure Appl. Chem. 61, 725-68 (1989), Table I, p. 730.