318.2 - When two cyclic systems are directly linked by a carbonyl group and another group is also present that has priority for citation as principal group, the compound is named by one of the following methods: (a) The cyclic component having the larger number of groups with such priority is named as parent and the other is named as part of an acyl group substituted in it. (b) If the ring systems are identical and have the same number of groups with such priority the nomenclature for assemblies of identical units (Subsection C-0.7) is used with the name "carbonyl" to denote the bivalent >CO radical. (c) If different cyclic components have the same number of groups with such priority, the senior ring system is named as parent and the other is named as part of an acyl group substituted in it.
Examples to Rule C-318.1
Trivial names of radicals (see c above)
See Recommendations'93 R-5.6.2
Examples to Rule C-318.2
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