Short Notations for Organic Cation Classes

by Axel Drefahl • www.axeleratio.com

Short formula-like notations for organic cation classes support efficient search of information about cations and their salts by specifying selected substructural parts of the cation structure. Herein, notations for frequently occurring cation classes are described. These notations can be used in the Chemical Property Viewer to find members of classes of Ionic Liquids and Solids.
A common way of classifying multi-atomic cations such as many organic cations is by specifying the core structure of the cation and the side-chains attached to it. Typical acyclic core structures are NH3, NH2, NH, and N in primary, secondary, tertiary, and quaternary ammonium ions, respectively. Similar notations are derived for phosphonium and arsonium ions in which N is replaced by P or As.
Common cyclic core structures are heterocyclic rings. We use two upper-case letters to denote the most common ring cations:
Notation Name Charge Ring type
IM Imidazolium 1+ 5-ring, semi-aromatic
MO Morpholinium 1+ 6-ring, non-aromatic
PL Pyrrolidinium 1+ 5-ring, non-aromatic
PN Pyrrolinium 1+ 5-ring, non-aromatic
PP Piperidinium 1+ 6-ring, non-aromatic
PY Pyridinium 1+ 6-ring, aromatic

Hint
A similar page for anions is avaiable :
Short Notations for Anion Classes

Cation class notations are completed by placing side-chain symbols in front. The symbol R is used for alkyl groups including linear and branched chains. For cations with acyclic core structures, containing only one atom to which side-chains can be attached, the symbol R followed by an integer indicating the number of attachee alkyl groups is placed in front of the core structure notation:
ExampleCation class name
RNH3alkylammonium
R4Ptetraalkylphosphonium
R3Strialkylsulfonium
This notation does not distinguish between alkyl groups of different size or degree of branching. Tetramethylammonium and isobutyltrimethylammonium, for example, are both members of the class denoted by R4N.
In the case of cyclic core structures, the position of the ring substitution has to be given for each side-chain. The position integer precedes the symbol of the substituent:
ExampleCation class name
1R2R3RIM1-alkyl-2-alkyl-3-alkylimidazolium
1R1RPL1-alkyl-1-alkylpyrrolidinium
4RMO4-alkylmorpholinium (equal to N-alkylmorpholinium)
Last update was made on March 28 in 2008 by Axel Drefahl
Please, email comments and suggestions to axeleratio@yahoo.com