FR-8 Bridged Fused Ring Systems

Contents of Section

FR-8. Bridged Fused Ring Systems
FR-8.1 Procedure for naming bridged systems
FR-8.1.1 Selection of bridge
FR-8.1.2 Naming of ortho- or ortho- and peri-fused portion
FR-8.1.3 Order of citation of bridges
FR-8.2 Selection of fused ring system to be bridged

Continue with FR-8.3 Naming of Bridges

FR-8.1 Procedure for naming bridged systems

This section provides an outline of the procedure for naming bridged polycyclic fused ring parent hydrides.

FR-8.1.1 Selection of bridge

If a polycyclic skeleton cannot be completely named as a fused ring system then possible ways of naming the skeleton as a bridged fused ring system are considered. The bridge is selected as described in FR-8.2 to give the preferred fused ring system.

FR-8.1.2 Naming of ortho- or ortho- and peri-fused portion

The skeleton of the portion of the structure which remains after removal of the bridge(s) is named following FR-4. Note that the maximum number of non-cumulative double bonds is assigned after insertion of the bridge. Hence in order to allow for the necessary free valencies to the bridge the fused ring system may differ from the isolated fused ring system in the number of non-cumulative double bonds (see FR-9.1) and/or the need for indicated hydrogen (see FR-9.3). If needed indicated hydrogen is used to identify the required isomer (see FR-9).

Examples:

4a,8a-propanoquinoline

1,5-methanoindole
CAS name 1,5-methano-1H-indole

9H-9,10-ethanoacridine

9H-9,10-(ethanylylidene)anthracene
Beilstein name 9H-9,10-epiethanylylidene-anthracene

FR-8.1.3 Order of citation of bridges

Bridges are cited by the technique described in FR-8.4. If there is more than one independent bridge they are cited in alphabetical order (see FR-8.4.1) unless identical (see FR-8.4.4). Dependent bridges are cited in front of all independent bridges. If there is a choice of attachment locants see FR-8.4.3.

FR-8.2 Selection of fused ring system to be bridged

The bridge (or bridges) is selected which results in the preferred fused ring system remaining by the following criteria applied in order. For the following examples see Note 3 to FR-1.4 on double bonds.

a. The fused ring system before bridging containing the maximum number of rings.

Example:

not
1H-1,3-propanocyclobuta[a]indene (fused ring system has 3 rings)
not 8,10,1-(ethane[1,1,2]triyl)benzo[8]annulene (fused ring system has 2 rings)
Beilstein name 6,7,8,9-tetrahydro-1,9-cyclo-cycloocta[cd]indene

Note

Both structures have the same carbon skeleton although different numbers of double bonds.

b. The fused ring system including the maximum number of skeletal atoms.

Example:

6,7-(prop[1]en[1]yl[3]ylidene)benzo[a]cyclohepta[e][8]annulene
not 7,6-(prop[1]en[1]yl[3]ylidene)benzo[a]cyclohepta[e][8]annulene (moves double bonds)
nor 4,5-buta[1,3]dienodibenzo[a,d][8]annulene
nor 6,10,15-(methanediylylidene)benzo[15]annulene (criterion a)

c. The arrangement having the minimum number of heteroatoms in the fused ring system.

Example:

not
1,3-epoxynaphthalene not 1,3-(metheno)isochromene

Note

CAS and Beilstein prefer the heteroatoms in the fused ring portion. Hence they call this example 1,3- metheno-1H-2-benzopyran and 1,3-methenoisochromene respectively.

d. The most preferred fused ring system, according to FR-2.3 applied to the whole fused ring system.

Examples:

not
1,7-ethano[4,1,2]benzoxadiazine not 4,6-ethanopyrido[1,2-d][1,3,4]oxadiazine
(1,2,4 preferred to 1,3,9, see FR-2.3.h)

not
1,12-ethenobenzo[4,5]cyclohepta[1,2,3-de]naphthalene not 1,12-ethenobenzo[c]phenanthrene
(7,6,6,6 rings preferred 6,6,6,6 rings, see FR-2.3.c)

e. The number of composite bridges being minimised.

Example:

not
6,12-epoxy-5,13-methanobenzo[4,5]cyclohepta[1,2-f]isochromene
not 7,5,13-(epoxymethanetriyl)benzo[4,5]cyclohepta[1,2-f]isochromene

f. The number of dependent bridges being a minimum.

Example:

not
6,11-buta[1,3]dieno-3,8-phosphano[1,4]diazocino[2,3-g]cinnoline
not 3,15-phosphano-6,11-buta[1,3]dieno[1,4]diazocino[2,3-g]cinnoline

g. The number of atoms in dependent bridges being a minimum.

Example:

6,17-methano-10,13-pentanonaphtho[2,3-c][1]benzazocine
not 13,17-ethano-6,10-butanonaphtho[2,3-c][1]benzazocine
nor 10,17-ethano-6,13-butanonaphtho[2,3-c][1]benzazocine

h. The number of bivalent bridges (see FR-1.4.3) being a maximum. Similarly '-ylylidene' is preferred as a trivalent bridge to '-triyl' etc. (i.e. '-diyl' is preferred to '-ylylidene', '-triyl', '-diylidene', '-diylylidene' or '-tetrayl', etc.).

Examples:

not
2,6:5,7-dimethanoindeno[7,1-bc]furan not 5,7,2-(ethane[1,1,2]triyl)indeno[7,1-bc]furan

not
8,7-(azenoetheno)cyclohepta[4,5]cycloocta[1,2-b]pyridine
not 8,7-(azenoethanediylidene)cyclohepta[4,5]cycloocta[1,2-b]pyridine

i. The location of bridges which results in the preferred attachment locants firstly for independent bridges then dependent bridges.

Example:

5,14-(metheno)-2,3,4-(prop[2]en[1,3]diyl[1]ylidene)dicyclopenta[f,f']pentaleno[1,2-a:6,5-a']dipentalene
not 5,14-(metheno)-2,4,3-(prop[2]en[1,3]diyl[1]ylidene)dicyclopenta[f,f]pentaleno[1,2-a:6,5-a']dipentalene
See also FR-1.4 Note 2.

Note

This ring system appears to have a ring in the middle which is not named. The ten-membered ring is created by the bridges on the fully specified fused ring system.

j. The fused ring system which gives the lowest locant(s) for the principal characteristic group.

Example:

1,2,3,4-tetrahydro-1,4-ethenoanthracen-2-ol
not 1,4-dihydro-1,4-ethanoanthracen-11-ol

k. The fused ring system being chosen which includes the maximum number of non-cumulative double bonds.

Example:

1,4-dihydro-1,4-ethanoanthracene
not 1,2,3,4-tetrahydro-1,4-ethenoanthracene

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