The skeletal replacement ("a") nomenclature operation (refs. 1a, 2a) involves the exchange of one group of atoms, usually -CH2- or >CH-, or an atom, usually a carbon atom, for another group or atom. It is a way of introducing heteroatoms into rings, ring systems, or chains; the heteroatoms usually belong to elements in Groups 13, 14, 15, and 16 of the Periodic Table. This replacement operation transforms an acyclic or cyclic hydrocarbon into a heteroacyclic or heterocyclic system. Skeletal replacement is always applied to parent hydrides. The result is the formation of new parent hydrides (secondary parent hydrides) from hydrocarbon parent hydrides (primary parent hydrides).
The skeletal replacement operation can be applied as well to phane parent hydrides (primary parent hydrides) to create new phane parent hydrides (secondary parent hydrides). With phane parent hydrides, skeletal replacement nomenclature is applied in two ways:
(a) to indicate heteroatoms in heterocyclic amplificants whose names cannot be used as amplification prefix names because they, themselves, are named by replacement nomenclature (see PhI-2.2.1.2);(b) to name phane parent hydrides having heteroatoms located in the simplified parent skeleton, i.e., heteroatoms not in names of amplification prefixes.
PhI-4.1. Name Construction
A phane parent hydride name is constructed in accordance with the principles, conventions, and rules of phane nomenclature as described in PhI-1, PhI-2, and PhI-3. All rings and ring systems of the phane parent hydride that qualify as amplificants (see PhI-2.2.1) and hydrocarbon analogs for any heterocycles that do not qualify as amplificants because skeletal replacement ("a") nomenclature must be used to form their names are analyzed together in order to apply the various rules regarding priority of rings and ring systems and attachment locants described in PhI-3. A phane parent hydride name is then assembled, using allowed names for amplificants and hydrocarbon names for those amplificants whose names require the use of skeletal replacement ("a") nomenclature. Then, "a" prefixes for amplificants that require skeletal replacement nomenclature and for heteroatoms located in the simplified parent skeleton, are introduced into the name in front of the name of the first cited amplificant.
Locants designating the "a" prefixes are of two types depending on the location of the heteroatoms they describe. When the heteroatoms are not part of an amplificant their locants are simply those of the simplified phane parent skeleton. In the name 2,7-dithia-1(2,5)-thiophena-5(1,3)-cyclohexanacycloocta-phane (see Example 26), the locants "2" and "7" assigned to "dithia" are those of the simplified parent skeleton. When the heteroatoms are in an amplificant whose name requires the use of skeletal replacement nomenclature, their locants are the same as those described in PhI-3.3.1 for substituents, i.e., they are composed of the locant designating the amplificant in the simplified skeleton (the superatom) and a superscript locant indicating the position of the heteroatom in the amplificant. In the name 12,53-dioxa-3(2,5)-furana-1,5(1,6)-dicyclododecanacycloundcaphane (see Example 29), the locants "12" and "53" assigned to "dioxa" are locants denoting heteroatoms in the cyclododecane amplificants. Skeletal replacement ("a") prefixes and their locants are cited in the name in the usual order of their priority (refs. 1m, 2m, 19a), i.e., O > S > Se > Te > N, etc., and locants for the same heteroatom are cited in ascending order of their locants, first according to the primary skeletal (superatom) locant, and then according to the increasing numerical value of the superscript numbers (see PhI-3.3.3).
PhI-4.2. Skeletal Replacement ("a") Nomenclature in Simplified Skeletal Names
Skeletal replacement in simplified phane skeletal names is a normal skeletal replacement operation. The locants designating the position of the heteroatoms are those used to number the simplified parent skeleton. Such skeletal replacement names are constructed in two steps:
Step 1: The name of the phane parent hydride without heteroatoms except those in allowable amplificants (see PhI-2.2.1) is constructed;Step 2: Skeletal replacement ("a") nomenclature is applied to describe heteroatoms in the phane parent hydride name formed in step 1. Locants for the heteroatoms are assigned according to the numbering of the simplified parent skeleton and cited together with the corresponding replacement ("a") prefixes in front of the name of the first cited amplificant.
Example 21.
Step 1: 1,9(1),3,5,7(1,4)-pentabenzenanonaphaneStep 2: 2,4,6,8-tetraaza-1,9(1),3,5,7(1,4)-pentabenzenanonaphane
Example 22.
Step 1: 1(3,5)-1,2-oxazola-5(1,4)-cyclohexanacyclooctaphaneStep 2: 3,7-dithia-1(3,5)-1,2-oxazola-5(1,4)-cyclohexanacyclooctaphane
PhI-4.3. Skeletal Replacement ("a") Nomenclature in Amplificants
Some heterocyclic rings and ring systems can be only named by using skeletal replacement nomenclature, for example, heteromonocyclic rings having more than ten ring members (ref. 1n), heteropolycyclic compounds named by the extended von Baeyer system (refs. 1o, 2n, 15), heterospiroalkanes (refs. 1f, 1g, 2o, 16), and heteropolycyclic compounds whose names cannot be formed by fusion nomenclature (ref. 18). When present in a phane parent hydride as amplificants, these heterocycles must be named as hydrocarbons and the heteroatoms described by skeletal replacement nomenclature applied after construction of the phane parent hydride name. Therefore, naming of such phane parent hydrides proceeds in two steps:
Step 1: The name of the primary phane parent hydride is constructed based on allowed names for amplificants and hydrocarbon names for those heterocycles whose names are not allowed (PhI-2.2.1);Step 2: Skeletal replacement ("a") nomenclature is applied to describe heteroatoms that are not included in the name of the phane parent hydride formed according to step 1. Locants for the heteroatoms are assigned according to the numbering of the simplified skeleton and the positions of the heteroatoms in the amplificants following the instructions in PhI-3.3 for substituents. Thus, positions of heteroatoms in amplificants are described by composite locants.
Example 23.
Step 1: 3(1,10)-cyclooctadecana-1,5(1,3)-dibenzenacyclooctaphaneStep 2: 34,37,313,316-tetraoxa-31,310-diaza-(1,10)-cyclooctadecana-1,5(1,3)-dibenzenacyclooctaphane
PhI-4.4. Simultaneous Skeletal Replacement in Amplificants and Simplified Skeletal Names
When skeletal replacement occurs in both amplificants and simplified skeletons, both PhI-4.2 and PhI-4.3 are applied.
Example 24.
Step 1: 3(1,10)-cyclooctadecana-1,5(1,3)-dicyclohexanacyclooctaphaneStep 2: 34,37,313,316,7-pentaoxa-31,310-diaz-3(1,10)-cyclooctadecana-1,5(1,3)-dicyclohexanacyclooctaphane
Example 25.
Step 1: 1(1,4)-bicyclo[2.2.1]heptanacyclohexadecaphaneStep 2: 17,3,6,9,12,15-hexaoxa-1(1,4)-bicyclo[2.2.1]heptanacyclohexadecaphane
(1) International Union of Pure and Applied Chemistry. Organic Chemistry Division. Commission on Nomenclature of Organic Chemistry, A Guide to IUPAC Nomenclature of Organic Compounds, Recommendations 1993, R. Panico, W. H. Powell and Jean-Claude Richer (Senior Editor), Blackwell Scientific Publications, Oxford, 1993, 190 pp. (a) R-1.2.2.1, p. 23; R-2.3.3.2, p. 43; R-5.5.4.3, p. 95. (b) R-0.2.4.2, p. 17. (c) R-2.4.2.1, especially footnote 29, p. 49. (d) R-2.4.3, p. 51. (e) R-2.4.2, pp. 49-51. (f) R-2.4.3.1, pp. 51-2. (g) R-2.4.3.2, p. 52. (h) R-0.1.8, p. 10. (i) R-2.3.1.2, p. 39; R-2.3.3 (in part), pp. 40-4; R-2.4.1, pp. 44-9. (j) R-2.4.1.2, p. 46. (k) R-2.3.1.1, p. 39; R-2.3.3 (in part), pp. 40-4. (m) R-9.3, p.182. (n) R-2.3.3.2, p. 43. (o) R-2.4.2, pp. 49-51.
(2) International Union of Pure and Applied Chemistry. Organic Chemistry Division. Commission on Nomenclature of Organic Chemistry, Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H, 1979 Edition, J. Rigaudy and S. P. Klesney eds., Pergamon Press, Oxford 1979, 559 pp. (a) B-4, pp. 68-70; C-0.6, pp. 123-7; D-1.6, pp. 334-6; D-5.17, p. 388; D-6.71, pp. 419-20. (b) A-2.6, p. 10, footnote; C-13.11(e), p. 99, footnote; D-4.14, p. 374, footnote. (c) A-31.1, p. 31, especially its footnote. (d) Spiro hydrocarbons, p. 37, especially its footnote. (e) A-31.1 and A-31.2, p. 31; A-32, pp. 32-4. (f) A-41.1 and A-41.2, p. 38. (g) A-41.6, p. 39. (h) C-16.11, p. 108. (i) A-11.3, pp. 16-17 (benzene); A-21 and A-22, pp. 20-7; B-2 (in part) and B-3, pp. 55-68. (j) A-34, pp. 35-7; B-15 (in part), pp. 75-6. (k) (15) International Union of Pure and Applied Chemistry. Division of Organic Chemistry. Commission on Nomenclature of Organic Chemistry, "Extension and Revision of the von Baeyer system for Naming Polycyclic Compounds (Including Bicyclic Compounds)", in preparation.
(16) International Union of Pure and Applied Chemistry. Division of Organic Chemistry. Commission on Nomenclature of Organic Chemistry, "Extension and Revision of the Nomenclature for Spiro Compounds", in preparation.
(18) International Union of Pure and Applied Chemistry. Division of Organic Chemistry. Commission on Nomenclature of Organic Chemistry, "Nomenclature of Fused and Bridged Fused Ring Systems (Recommendations 1998)", Pure Appl. Chem. 1998, 70, 143-216.
(19) International Union of Pure and Applied Chemistry. Organic Chemistry Division. Commission on Nomenclature of Organic Chemistry, "Revision of the Extended Hantzsch-Widman System of Nomenclature for Heteromonocycles (Recommendations 1982)", Pure Appl. Chem. 1983, 55, 409-16. (a) Table 1, p. 413.
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