Contents of Section
2.2 Heterocyclic components
2.2.1 Heteromonocyclic components
2.2.2 Heteranthrene components
2.2.3 Pheno....ine components
2.2.4 Diazanaphthalene and diazaphenanthrene components
2.2.5 Trivially named polycyclic, nitrogen-heterocyclic components
2.2.6 Components formed by replacement of nitrogen by arsenic or phosphorus
2.2.7 Trivially named polycyclic, chalcogen-heterocyclic components
2.2.8 Heterobicyclic components with a benzene ring
References for this Section
Continue with FR-2.3 Priority order of Component Ring Systems.
Heterocyclic parent components are listed in Appendix 2. The components are listed in decreasing order of preference (see FR-2.3).
FR-2.2.1 Heteromonocyclic components
a. The following trivial names are retained for heteromonocyclic parent components. The reference numbers refer to the entry in Appendix 2.
In an attached component prefix the terminal 'e' is changed to 'o' (or the 'o' is added in the case of pyran and chalcogen analogues). Only the following abbreviated forms are used:
|furo from furan||pyrimido from pyrimidine|
|imidazo from imidazole||thieno from thiophene|
|pyrido from pyridine|
These abbreviated forms are also used in combined forms e.g. benzofuro (see FR-2.2.8).
1. In the previous edition of these rules oxazole, isoxazole, thiazole and isothiazole were used as component names. When combined in heterobicyclic names with a benzene ring (FR-2.2.8) locants were required for the iso case. The full Hantzsch-Widman name is now recommended for fusion names i.e. 1,3-oxazole, 1,2-oxazole, 1,3-thiazole and 1,2-thiazole respectively. The traditional names are retained in these recommendations for use with the isolated ring system and are still used as fusion components by CAS and Beilstein together with selenazole, isoselenazole, tellurazole and isotellurazole.
2. Beilstein uses selenopyran and telluropyran instead of selenine and tellurine.
b. A heteromonocyclic parent component with a ring of up to ten members not listed in FR-2.2.1(a) is named using the extended Hantzsch-Widman system (ref 9). In an attached component prefix the terminal 'e' is changed to 'o'. In fused ring names where locants are needed to locate the heteroatoms in a component ring these locants are cited in square brackets (see FR-4.8).
1. In the Hantzsch-Widman system (ref 9) the terminal 'e' is optional. In this document the 'e' is included. If the 'e' is omitted the terminal '-in' is changed to '-ino'.
2. The Hantzsch-Widman suffix is that appropriate for a mancude (maximum number of non-cumulative double bonds) ring system.
c. A heteromonocyclic parent component with more than ten members is named by modifying the corresponding heterocycloalkane name changing the ending '-ane' to '-ine'. In an attached component prefix the terminal 'e' is changed to 'o'. If locants are needed to locate the heteroatoms these are cited in square brackets (see FR-4.8). Where there is a choice of locants they are selected as in the Hantzsch-Widman system.
When a heteromonocyclic component with more than ten members is present Beilstein uses replacement nomenclature. Thus the example above is called 3,6-dioxa-10,14,17-triaza-cycloheptacyclopentadecene by Beilstein.
FR-2.2.2 Heteranthrene components
A heterotricyclic parent component that consists of two benzene rings fused to a 1,4- diheterabenzene in which the heteroatoms are the same is named from the appropriate replacement prefix (Table 1 of RB-1.1 in ref 9) and the suffix '-anthrene' with elision of the 'a'.
In an attached component prefix the ending '-ene' is changed to '-eno'.
Appendix 2 includes this system for O, S, Se, Te, P, As, Si, B, and Hg (entries 63, 74, 79, 84, 89, 99, 109, 110, and 111 in appendix 2). The nitrogen analogue is an exception and is named phenazine. Boranthrene, oxanthrene, silanthrene and telluranthrene were not included previously (ref 3). Oxanthrene is still called dibenzo[1,4]dioxin by CAS and Beilstein. Mercuranthrene, formerly called phenomercurin (ref 3) or phenomercurine (ref 3a), is called cyclo-di- -1,2-phenylenedimercury by CAS.
FR-2.2.3 Pheno....ine components
A heterotricyclic parent component that consists of two benzene rings fused to a 1,4- diheterabenzene in which the heteroatoms are different is named by adding the prefix 'pheno-' to the Hantzsch-Widman name (ref 9).
In an attached component prefix the ending '-ine' is changed to '-ino' (see note 1 to FR- 2.2.1.b).
Appendix 2 includes this system for NH with O, S, Se and Te (entries 1-4); N with P, As and Hg (with the reverse order of 'a'-prefixes for entries 5-7); O with S, Se, Te, PH, AsH and SbH (entries 57-62); and S with AsH (entry 73). Phenoxastibinine was previously called phenoxantimonine. 2H-Phenomercurazine, formerly called 2H-phenomercazine, is called (3,6-cyclohexadien-1-yl-2-ylidenenitrilo-1,2-phenylene)mercury by CAS.
FR-2.2.4 Diazanaphthalene and diazaphenanthrene components
A heterocyclic component which corresponds to naphthalene or phenanthrene where each terminal ring has one non-fusion atom replaced by nitrogen is called naphthyridine or phenanthroline respectively. The location of the two nitrogen atoms is indicated by the appropriate locants [see Appendix 2 for the range of isomers possible for naphthyridine (entries 27-30, 32 and 33) and phenanthroline (entries 9-18)].
Phenanthroline is numbered in the standard way (see FR-5.3) despite the non-standard numbering of phenanthrene.
FR-2.2.5 Trivially named polycyclic, nitrogen-heterocyclic components
The following trivial names of nitrogen heterocycles are also used as parent components in fusion nomenclature. In an attached component prefix the terminal 'e' is changed to 'o' e.g. indolo (from indole). The reference numbers below refer to Appendix 2.
1. Rule B-3.3 (ref 3) recommended the abbreviation of isoquinolino to isoquino and quinolino to quino. These abbreviated forms are not used here but are still used by CAS and Beilstein.
2. -Carboline (pyrido[3,4-b]indole) was abandoned as a component name in 1979 (ref 3).
3. Acrindoline, anthrazine, anthyridine, phenanthrazine, phthaloperine, quindoline, quinindoline, thebenidine, triphenodioxazine and triphenodithiazine are used as component names by CAS (see note a of appendix 2).
4. 1-Pyrindene (cyclopenta[b]pyridine) and 2-pyrindene (cyclopenta[c]pyridine) are used by CAS and Beilstein for the isolated ring system but not as a component for fusion.
FR-2.2.6 Components formed by replacement of nitrogen by arsenic or phosphorus
The following parent components containing arsenic or phosphorus are named by adaption of the corresponding nitrogenous parent component names. The reference number refers to the entry in Appendix 2.
In an attached component prefix the terminal 'e' is changed to 'o'.
FR-2.2.7 Trivially named polycyclic, chalcogen-heterocyclic components
The following trivial names of chalcogen heterocycles are also used in fusion nomenclature. The reference number refers to Appendix 2.
In an attached component prefix the terminal 'e' is changed to 'o', e.g. xantheno (from xanthene).
Chromene and isochromene and the chalcogen analogues are not used by CAS but are used by Beilstein. CAS uses 1-benzopyran, 2-benzopyran etc.
FR-2.2.8 Heterobicyclic components with a benzene ring
Unless listed as a trivially named heterobicycle in Appendix 2 a benzene ring fused to a heteromonocycle of five or more members (a benzoheterocycle) is named by prefixing number locants indicating the position(s) of the heteroatom(s) to benzo followed by the trivial, Hantzsch-Widman, or modified replacement name (see FR-2.2.1) of the heteromonocycle without locants. The locants quoted correspond to the numbering of the bicyclic structure, which follows FR-5.4. Locants are not needed if their omission does not result in ambiguity, e.g. benzimidazole, benzotriazole. As an exception to FR-4.7 the 'o' of benzo is elided if followed by a vowel. See FR-3.5 for the use of this type of name as a component and FR-4.8 for the use of square brackets around locants. Brackets are not used for the unmodified ring system.
Names of this type are only used as components under certain conditions; see FR-3.5 for the details. Beilstein does not use this type of name.
1. 1-Benzofuran and 2-benzofuran were formerly called benzofuran and isobenzofuran (ref 3) and may still be used for the isolated ring system. CAS still uses benzofuran and isobenzofuran as fusion components.
2. 1,2-Benzoxazole and its 2,1- and 1,3-isomers and chalogen analogues were called 1,2- benzisoxazole, 2,1-benzisoxazole, benzoxazole, etc. These are still used by CAS for the isolated ring system and as fusion components.
3. IUPAC Nomenclature of Organic Chemistry, Sections A and B, 1st edition, 1958; 2nd edition, 1966; 3rd edition (combined with section C), 1971; 4th edition (combined with sections C, D, E, F and H), 1979.
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.
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