Free Radicals, Ions, and Radical Ions

Cations Rule C-83

83.1 - When a cation can be considered as formed by loss of an electron or electrons from a radical at the free valence position(s) it may be named (a) by adding the word "cation" to the radical name or (b) by replacing the suffix "-yl" of the univalent radical by "-ylium". Method (b) can be extended to multivalent cations by using the suffixes "-diylium", "-triylium", etc., attached to the name of a hydrocarbon or heterocyclic system. The name "carbenium" may be used for .

Examples to Rule C-83.1

(a) Ethyl cation
(b) Ethylium or Ethenium (Rule C-82.4)

(a) Phenyl cation
(b) Phenylium

(a) 2-Cyclohexen-1-yl cation
(b) 2-Cyclohexen-1-ylium

(a) 9-Anthryl cation
(b) 9-Anthrylium

(a)Neopentyl cation
(b) Neopentylium

(a)Triphenylmethyl cation
(b) Triphenylmethylium or

(a) Cyclopropenyl cation
(b) Cyclopropenylium

(a) Methylene dication
(b) Methanediylium

(a) Ethylidene dication
(b) Ethane-1,1-diylium

(a) Ethylene dication
(b) Ethane-1,2-diylium

(a) Acetyl cation
(b) Acetylium

(a) Methylsulfanyl cation or
Methanesulfenyl cation
(b) Methylsulfanylium or

(a) Methanesulfonyl cation
(b) Methanesulfonylium

(a) Benzylideneaminyl cation
(b) Benzylideneaminylium

(a) Quinolizinyl cation; (b) Quinolizinyum

(a) 1,2,3-Benzodithiazolyl cation;
(b) 1,2,3-Benzodithiazolylium

Note 1: Method (a) may be used for the isolated species, and method (b) for salts and for the corresponding substituents with names ending in "-io". Greater precision may be necessary for resonating structures; e.g., for univalent cations, two types of case may occur.

(i) Neither double-bond specification nor indication of hydrogen is necessary for the parent compound, as, for instance, for benzene or anthracene; but it may be necessary to indicate which hydrogen atom has been removed and this is done by the locant in names such as 9-anthryl cation and 9-anthrylium.

(ii) Double-bond specification or indication of hydrogen is necessary for the parent compound. Then use of the "-ylium" ending, without a locant, shows that such specification is not needed for the ionic species because the hydrogen atom removed is that which would have been specified as "indicated hydrogen". This applies also when a CH2 group in conjugated polyenes is located indirectly by locants for double bonds. The following names, for instance, are thus unambiguous:

Note 2: According to Rules A-21 and B-3, parent compounds for ortho-fused, or ortho- and peri-fused, hydrocarbons and heterocycles are chosen so as to contain the maximum number of non-cumulative double bonds. This principle has sometimes been applied to heterocyclic ions and leads, for instance, to the following names (contrast example above):

83.2 - The following are examples of well-established trivial names of cations that are retained as exceptions:

83.3 - Cation radicals that can be considered to be formed by addition of a proton to a radical may be named (a) by adding the word "cation" to the name of the compound having the same formula or (b) by adding the suffix "-yl" to the name of the cation.

Examples to Rule C-83.3

(a) Ethane cation
(b) Ethaniumyl

(a) Benzene cation
(b) Benzeniumyl

(a) Pyrazine 1-cation
(b) 1-Pyraziniumyl

(a) Quinoline 1-cation
(b) 1-Quinoliniumyl

(a) Tri-p-tolylamine cation
(b) Tri-p-tolylammoniumyl

(a) Dimethylsulfane cation
(b) Dimethylsulfoniumyl

See Recommendations'93 R-5.8.2

Rule C-84
Two or More Kinds of Ionic Centre with the Same Kind of Charge in a Single Structure
Rule C-85
Rule C-86
Positive and Negative Ionic Centres in a Single Structure
Rule C-87


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