FR-2.3 Priority Order of Component Ring Systems

Contents of Section

FR-2.3 Priority order of component ring systems
FR-2.4 Natural products and fullerenes
References for this Section

Continue with FR-3 Construction of Fusion Names.

Selection of a parent component (see FR-3.3) or attached component (see FR-3.4) is based on the following rules which are applied in order. Appendices 1 and 2 list the hydrocarbon and heterocyclic components in decreasing order of preference. If there is a choice, the preferred component should be:

a. A heterocyclic component containing the heteroatom occurring earliest in the order N, F, Cl, Br, I, O, S, Se, Te, P, As, Sb, Bi, Si, Ge, Sn, Pb, B, Hg [see Table 1 of the revised Hantzsch-Widman system (ref 9) with the exception of nitrogen].

Examples:

azuleno[6,5-b]pyridine
(pyridine preferred to azulene)

chromeno[2,3-c]pyrrole
(pyrrole preferred to chromene)

2H-[1,4]dithiepino[2,3-c]furan
(furan preferred to dithiepine)

b. A component containing the greater number of rings.

Example:

6H-pyrazino[2,3-b]carbazole
(carbazole [3 rings] preferred to quinoxaline [2 rings])

c. A component containing the larger ring at the first point of difference when comparing rings in order of decreasing size.

Examples:

2H-furo[3,2-b]pyran
(pyran [6] preferred to furan [5])

naphtho[2,3-f]azulene
(azulene [7,5] preferred to naphthalene [6,6])

d. A component containing the greater number of heteroatoms of any kind.

Examples:

5H-pyrido[2,3-d][1,2]oxazine
(oxazine preferred to pyridine)

2H-furo[2,3-d][1,3]dioxole
(dioxole preferred to furan)

e. A component containing the greater variety of heteroatoms.

Examples:

[1,3]dioxolo[d][1,2]oxaphosphole
(O and P preferred to only O)

6H,8H-[1,2,4]dioxazino[4,3-c][1,3,2]oxazaphosphinine
(O, N and P preferred to O and N)

f. A component containing the greater number of heteroatoms most preferred when considered in the order F, Cl, Br, I, O, S, Se, Te, N, P, As, Sb, Bi, Si, Ge, Sn, Pb, B, Hg [i.e. Table I of the revised Hantzsch-Widman system (ref 9)].

Examples:

[1,3]selenazolo[5,4-d][1,3]thiazole
(S,N preferred to Se,N)

[1,4]oxaselenino[2,3-b][1,4]oxathiine
(O,S preferred to O,Se)

g. A component in the preferred orientation according to FR-5.2.

Examples:

quinolino[4,3-b]acridine
(acridine [3 rings in row] preferred to phenanthridine [2 rings in row] FR-5.2.a)

benzo[pqr]tetraphene
(tetraphene [3 rings in row] preferred to chrysene or pyrene [2 rings in row] FR-5.2.a)

Note

The second example is called benzo[a]pyrene by CAS as an exception to this rule.

h. A component with the lower locants for heteroatoms. Example:

pyrazino[2,3-d]pyridazine
(pyridazine [1,2] preferred to pyrazine [1,4])

Note

Quinolizine is an exception to this rule in CAS where it is preferred to quinoline or isoquinoline.

i. A component with the lower locants for the heteroatoms when considered in the order F, Cl, Br, I, O, S, Se, Te, N, P, As, Sb, Bi, Si, Ge, Sn, Pb, B, Hg [i.e. Table I of the revised Hantzsch-Widman system (ref 9)].

Example:

3H,5H-[1,3,2]oxathiazolo[4,5-d][1,2,3]oxathiazole
(1,2,3preferred to 1,3,2)

j. A component with the lower locants for bridgehead carbon atoms.

Example:

indeno[1,7-kl]aceanthrylene
(aceanthrylene [2a] preferred to acephenanthrylene [3a])

FR-2.4 Natural products and fullerenes

Fusion of components to natural products and fullerenes are not included in this document. Details have been published for carbohydrates (ref 11), steroids (ref 12) and tetrapyrroles (ref 13) and there are proposals for prostaglandins, thromboxanes (ref 14), natural products in general (ref 15) and fullerenes (ref 16).

3a. A Guide to IUPAC Nomenclature of Organic Compounds, Recommendations 1993, Blackwell Scientific Publications, 1993.

9. IUPAC, Revision of the extended Hantzsch-Widman system of nomenclature for heteromonocycles, Pure Appl. Chem. 55, 409-416 (1983), see also ref 3a, pp. 40-44.

11. IUPAC-IUBMB Nomenclature of carbohydrates, Pure Appl. Chem. 68, 1919-2008 (1996)

12. IUPAC-IUB, Nomenclature of steroids, Eur. J. Biochem. 186, 429-458 (1989); Pure Appl. Chem. 61, 1784-1822 (1989).

13. IUPAC-IUB, Nomenclature of tetrapyrroles, Pure Appl. Chem. 59, 779-832 (1987); Eur. J. Biochem. 178, 277-328 (1988).

14. Nomenclature of prostaglandins and thromboxanes, in preparation by JCBN.

15. Revision of section F, in preparation by CNOC.

16. IUPAC, Nomenclature and terminology of fullerenes: a preliminary survey, Pure Appl. Chem. 69, 1411-1434 (1997).

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