"Seniority" in respect to spiro compounds is based on the principles:

(i) an aggregate is senior to a monocycle;

(ii) of aggregates, the senior is that containing the largest number of individual rings;

(iii) of aggregates containing the same number of individual rings, the senior is that containing the largest ring;

(iv) if aggregates consist of equal numbers of equal rings the senior is the first occurring in the alphabetical list of names.

This HTML reproduction of Sections A, B and C of IUPAC "Blue Book" is as close as possible to the published version [see Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H, Pergamon Press, Oxford, 1979. Copyright 1979 IUPAC.] If you need to cite these rules please quote this reference as their source.

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