FR-3.4 Selection of attached component(s)

Contents of Section

FR-3.4 Selection of attached component(s)
FR-3.4.1 Order of preference between attached components
FR-3.5 Heterobicyclic compounds with a benzene ring as a component
FR-3.6 Order of citation of fusion prefixes

Continue with FR-4 Fusion Descriptors.

After selection of the parent component (or parent components and interparent component(s) if a multiparent name is selected - see FR-6) other rings are identified as far as possible as attached components. If there are alternative first-order attached components FR-2.3 is used to select the preferred component.

Example:

8H-cyclopenta[3,4]naphtho[1,2-d][1,3]oxazole
not 8H-benzo[6,7]indeno[5,4-d][1,3]oxazole
(naphthalene preferred to indene)

If there are alternative locations for the first-order attached components, the criteria of FR-3.4.1 are used to select the preferred arrangement. After selection of the first-order attached components remaining rings are considered for second-order attached components and so on to higher-order attached components.

If there are alternative names which only differ in their fusion locants see FR-4.5 for the criteria to select the preferred name.

Note

Heterobicyclic components with a benzene ring named by FR-2.2.8 are only identified after this stage (see FR-3.5).

FR-3.4.1 Order of preference between attached components

If after consideration of the parent component there are two or more potential attached components, or two or more locations for an attached component, the following criteria are applied in order until a distinction is obtained. If a partial distinction is obtained the following criteria are only applied to distinguish between remaining choices. In the examples below the preferred attached component is marked with a complete box and the other location(s) with a dashed line.

a. The location that has preferred locants for fusion to the parent component as a set.

Example:

5H-benzo[6,7]cyclohepta[4',5']indeno[1',2':3,4]fluoreno[2,1-b]furan
not 5H-benzo[5',6']indeno[1',2':1,2]cyclohepta[7,8]fluoreno[4,3-b]furan
(1,2 preferred to 3,4)

b. The location that has preferred locants for fusion to the parent component in the order of citation.

Example:

naphtho[2',1':3,4]phenanthro[1,2-b]thiophene
not naphtho[2',1':3,4]phenanthro[2,1-b]thiophene
nor dibenzo[3,4:5,6]phenanthro[9,10-b]thiophene
(1,2 preferred to 2,1 and both preferred to 9,10)

c. The above procedure is continued exploring outwards to the preferred second-order attached components; preferred fusion locants between the first and second-order attached components; etc.

Example:

7H-pyrrolo[2",1":1',2']isoquinolino[4',3':4,5]cyclopenta[1,2-b]acrdine
not 7H-benzo[7',8']indolizino[6',5':4,5]cyclopenta[1,2-b]acridine
(isoquinoline preferred to indolizine)

FR-3.5 Heterobicyclic compounds with a benzene ring as a component

If the initially identified preferred components for naming the fused ring system include an isolated benzo component (i.e. not forming part of a component such as quinoline or naphthalene) ortho-fused to a heteromonocyclic component, these two components are treated together as a one-component unit (a 'benzoheterocycle'; see FR-2.2.8). However this approach should not be used if it disrupts a multiparent name (see FR-6) or the use of multiplicative prefixes (FR-4.9). The other initially identified preferred components should not be changed in any other way except in so far as the 'benzoheterocycle' may change the preference between components i.e. the use of a 'benzoheterocycle' component may change the order of attached components and may affect the choice of the preferred parent and/or attached component.

Examples:

thieno[3,2-f][2,1]benzothiazole
(2,1-benzothiazole is preferred to 1-benzothiophene)
CAS name thieno[3,2-f]-2,1-benzisothiazole
Beilstein name thieno[3',2':4,5]benzo[1,2-c]isothiazole

[1,3]benzoxazolo[6,5-g]quinoline
(quinoline preferred to benzoxazole)
CAS name benzoxazolo[6,5-g]quinoline
Beilstein name oxazolo[4',5':4,5]benzo[1,2-g]quinoline

benzo[1,2-b:4,5-c']difuran
not furo [3,4-f][1]benzofuran
(multiparent name preferred)

6H-benzo[c]chromene
CAS name 6H-dibenzo[b,d]pyran

10H-furo[3',2':4,5]indeno[2,1-b]pyridine
not [1]benzofuro[5',4':3,4]cyclopenta[1,2-b]pyridine
(pyridine preferred to benzofuran)
(indene must be used as a component)

4H-[1,4]thiazino[2,3-g]quinoline
not 4H-pyrido[2,3-g][1,4]benzothiazine
(quinoline must be used as a component)

7H-phenanthro[5,4,3-cdef][1]benzoxepine
Beilstein name 8H-1,12-etheno-benzo[e]naptho[1,8-bc]oxepine

9aH-pyrano[2,3-b][1]benzofuran
(pyran preferred to furan but benzofuran preferred to pyran)
CAS name 9aH-pyrano[2,3-b]benzofuran
Beilstein name 9aH-benzo[4,5]furo[2,3-b]pyran

thieno[3',2':5,6]phenanthro[4,3-e][1]benzothiophene
CAS name naphtho[1,2-e:8,7-e']bis[1]benzothiophene
Beilstein name thieno[2",3";5',6']benzo[1',2';5,6]phenanthro[3,4-b]thiophene

FR-3.6 Order of citation of fusion prefixes

Fusion between two components is indicated by the technique described in FR-4. All attached components are cited in front of the parent component(s). Each second-order attached component is cited in front of the first-order attached component to which it is fused and so on to higher-order attached components. If there are two or more different components, or sets of components, attached to a lower-order component they are cited in alphabetical order.

Examples:

furo[3,2-b]thieno[2,3-e]pyridine
(furo is before thieno)

furo[2',3':4,5]pyrrolo[2,3-b]imidazo[4,5-e]pyrazine
(fur-pyrrolo is before imidazo)

If the only distinction is between as-indacene and s-indacene then the italic characters are considered; otherwise they are treated as indacene for consideration of alphabetical order.

Example:

as-indaceno[2,3-b]-s-indaceno[1,2-e]pyridine

If two (or more) identical components are fused to a third they are cited together by the use of di- (or tri-, etc.) or bis- (or tris-, etc.) as described in FR-4.9. Use of a multiplicative prefix does not affect the alphabetical order of citation of components attached at the same level.

Examples:

difuro[3,2-b:3',4'-e]pyridine

5H-furo[3,2-g]dipyrano[2,3-b:3',4',5'-de]quinoline
(furo before dipyrano)

1H-cyclopropa[b]dicyclopenta[2,3:6,7]oxepino[4,5-e]pyridine
not 1H-dicyclopenta[2,3:6,7]oxepino[4,5-b]cyclopropa[e]pyridine
[cyclopropa is before dicyclopentaoxepino (treated as a unit)]

If two or more groups of components only differ by virtue of the fusion locants within the group then these are used to determine the order.

Example:

4H,16H,20H,26H-cyclopenta[4,5]oxepino[3,2-a]bis(cyclopenta[5,6]oxepino)-
[3',2'-c:2",3"-h]cyclopenta[6"',7"']oxepino[2"',3"'-j]phenazine

If two or more groups of components only differ by virtue of the heteroatom locants these are used to determine the order.

Example:

2H-[1,2]oxazolo[5,4-c][1,3]oxazolo[3,2-a]pyridine

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