60
1 Parent Structures
i) If all the preceding criteria fail, that component takes priority whose
hetero atoms had lowest position numbers and/or letters before fusion.
Pyrazino [2,3-d] pyridazine
3H,5H-[l,3,2]Oxathiazolo[4,5-d] [l,2,3]oxathiazole
The examples shown above clearly demonstrate that the general fusion
principles for heterocyclic systems fully resemble those for analogous
hydrocarbon systems. For two-ring systems containing a benzo unit, however, Chemical Abstracts and the Ring Index rigorously apply an exceptional rule which appears only as a subordinate alternative in the IUPAC
manuals. Here, only the heteroatoms and not the fusion positions are designated in accordance with the numbering principles outlined below. The
names thus formed can be used as (parent) component names for higher
fused systems.
N
1
~''''9u2
~--p3
[1,3,2] Benzoazaphosphacuprole
not: Benzo [d] [1 ,3,2]azaphosphacuprole
3H-[4,1,3]Benzoazarsasilepine
not: 3H-Benzo [e][ 1 ,4,2] azarsasilepine
If a central system is fused to two (or more) identical peripheral senior
components, name construction occurs as shown below:
4
6H,13H-[ 1,4]Dithiino[2,3-c: 5,6c']bis[ l]benzopyran