Alignment of principles for specifying ligands and substituent groups across various areas of nomenclature

During the review of the project on boron hydride nomenclature by the Chemical Nomenclature and Structure Representation Division, (Division VIII) in the first half of 2016, inconsistencies in the use of kappa (κ) symbols were noticed. Further, it became apparent that the approach followed until then, namely to use kappa terms at the end of a ligand name otherwise unchanged as compared to the non-ligated species, is not feasible. This raised the question of how to handle substituents in a ligand with different ligating atoms/kappa terms. The logical step was to look for precedent in similar situations, e.g., isotopically modified substituents. However, when comparing the possible approaches, it was further noticed that inconsistencies exist in the Blue Book concerning the treatment of substituents with different kinds of modification, specifically when lambda symbols, stereodescriptors, or isotopic modifications are added. The Blue Book task group had already decided that, in the alphabetical ordering of substituents, an unmodified substituent is always to be listed before the same, but modified substituent—the “nothing before something” principle approved by the Division Committee. With the return of this question, concerns about the consequences for numbering arose.

A project was initiated to provide the basis for the completion of several projects with different states of progress:

1. Boron hydride nomenclature (2012-045-1-800)

2. Metallacycles nomenclature (2013-030-1-800)

3. Preferred names for inorganic compounds (kappa document) (2006-038-1-800)

4. Blue Book revision and extension (2015-052-1-800)

5. Inorganic and coordination polymers (2011-035-1-800)

The task group will review the inconsistent sections in the Blue Book and sections on comparable situations in the Red Book and then find a consensus on:

1. the grouping of substituents or ligands with different kinds of modifications

2. the alphabetical order of substituents or ligands with different kinds of modifications

3. the positioning of locants for substituents and ligands in chemical names

4. the positioning and grouping of kappa terms in chemical names

For further information, contact the Task Group Chair Karl-Heinz Hellwich <hellwich.iupac@gmx.de> www.iupac.org/project/2017-033-1-800