Hello,
I have a question to the IUPAC nomenclature of heterocyclic compounds. Usually hydrogen atoms in the ring system not attached to atoms connected by double bonds are denoted as indicated hydrogen atoms.
Now I have a molecule (2,3-dimethyl-2H-indazol-6-amine) where a methyl group is located at position 2 and the name is "...2H-indazol...". So can the IUPAC rule be extended to "a position not connected by a double bond"? Since there is no H at the nitrogen at position 2...
Can anyone help me with a nice explanation of this special nomenclature case?
Thanks a lot.
Citation of indicated hydrogen
When a name applies equally to two or more isomeric systems with the maximum number of non-cumulative double bonds, and when the name can be made specific by indicating the position of one or more hydrogen atoms in the structure, this is accomplished by modifying the name with a locant, followed by an italic H for each of these hydrogen atoms. These atoms are called indicated hydrogen.
Notes
1. Indicated hydrogen is often omitted for the normally encountered isomer of some ring systems (see rule B-2.11 ref 3, and note a to Table 20 and 23 ref 3a) i.e. carbazole, fluorene, imidazole, indazole, indene, indole, isochromene, isoindole, perimidine, phenalene, phenothiazine, phenoxazine, purine, pyrazole, pyrrole, selenoxanthene, telluroxanthene, thioxanthene, xanthene.2. Indicated hydrogen may be omitted where there is no ambiguity. For example at a position located between two divalent atoms
Citation of indicated hydrogen
When a name applies equally to two or more isomeric systems with the maximum number of non-cumulative double bonds, and when the name can be made specific by indicating the position of one or more hydrogen atoms in the structure, this is accomplished by modifying the name with a locant, followed by an italic H for each of these hydrogen atoms. These atoms are called indicated hydrogen.
Notes
1. Indicated hydrogen is often omitted for the normally encountered isomer of some ring systems (see rule B-2.11 ref 3, and note a to Table 20 and 23 ref 3a) i.e. carbazole, fluorene, imidazole, indazole, indene, indole, isochromene, isoindole, perimidine, phenalene, phenothiazine, phenoxazine, purine, pyrazole, pyrrole, selenoxanthene, telluroxanthene, thioxanthene, xanthene.2. Indicated hydrogen may be omitted where there is no ambiguity. For example at a position located between two divalent atoms
Dear Benedikt Engel I think that Jürgen Wintner already provided a rather comprehensive answer to your question. Please see attached a schematic representation of your compound 2,3-dimethyl-2H-indazol-6-amine. The term "2H-indazol-" refers to the parent (unsubstituted= compound which has a hydrogen atom attached to N2. In the case of trivalent nitrogen, doubly-bonded N atoms cannot carry a hydrogen.
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