Substitutive Nomenclature

Rule C-14.1 Seniority of Ring System

14.11 - Seniority of ring systems is decided by applying the following criteria, successively in the order given, until a decision is reached:

(a) All heterocycles are senior to all carbocycles.

Example to Rule C-14.11(a)

(b) For heterocycles the criteria based on the nature and position of the hetero atoms set out in Rule B-3.1.

Examples to Rule C-14.11(b)

See Rule B-3.1, such as:

(c) Largest number of rings.

Example to Rule C-14.11(c)

(d) Largest individual ring at first point of difference.

Examples to Rule C-14.11(d)

(e) Largest number of atoms in common among rings.

Examples to Rule C-14.11(e)

Note: Rings joined by a link (single or double) are included in this choice only when identical and named by the bi-, ter-, quater-, etc., system (see Rule A-54.1).

(f) Lowest letters (a, b, etc., see Rule A-21.5) in the expression for ring junctions.

Example to Rule C-14.11(f)

(g) Lowest numbers at the first point of difference in the expression for ring junctions. (See Rules: A-21.5, for ortho-fusion and ortho-peri-fusion; A-32 for tricyclo, etc., systems; A-41, A-42, B-10, and B-11 for spirans; A-52 for assemblies of identical units.)

Examples to Rule C-14.11(g)

(h) Lowest state of hydrogenation.

Example to Rule C-14.11(h)

(i) Lowest locant for indicated hydrogen.

Example to Rule C-14.11(i)

senior to
senior to

(j) Lowest locant for point of attachment (if a radical).

Example to Rule C-14.11(j)

(k) Lowest locant for an attached group expressed as suffix.

Example to Rule C-14.11(k)

() Maximum number of substituents cited as prefixes.

(l) Lowest locant for substituents named as prefixes, hydro prefixes, -ene, and -yne, all considered together in one series in ascending numerical order independently of their nature.

Examples to Rule C-14.11(l)

(m) Lowest locant for that substituent named as prefix which is cited first in the name (see Subsection C-0.16)

Example to Rule C-14.11(m)

Note: Hydro and dehydro prefixes, if treated as detachable (see Rule C-16.11), are considered along with prefixes for substituents when this criterion is applied.

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