Retained name

In chemistry, a retained name is a name for a chemical that does not follow the rules of a systematic name, but that is still allowed as a name in that system. Retained names can be trivial names or part of an older system of names.

Normally retained names are older than the rules and are used so that new work uses the same names as older work.

 Examples 
The light alkanes all use retained names:  is methane (not carbane),  is ethane (not dicarbane),  is propane (not tricarbane), and  is butane (not tetracarbane). Systematic names are used for their structural analogues with heavier atoms, like disilane for .

Aromatic compounds and heterocyclic compounds commonly have retained names, as systematic names of these compounds that did not use retained names as a basis would be very complicated. Consider the following possible names for the common biomolecule purine (in its most common tautomer):
 Retained name 9H-purine Retained names for single cycles 7H-imidazo[4,5-d]pyrimidine Retained name for bicyclic parent 1H-1,3,4,6-tetraazaindene No retained names 2,4,7,9-tetraazabicyclo[4.3.0]nona-1,3,5,8-tetraene

 Sources 

Category:Chemical nomenclature