FR-4. Fusion Descriptors

Contents of Section

FR-4. Fusion Descriptors
FR-4.1 Identification of sides of parent components
FR-4.2 Identification of sides of attached components
FR-4.3 Fusion of a first-order attached component to the parent component
FR-4.4 Fusion of a higher-order attached component to an attached component
FR-4.5 Choice of locants

Continue with FR-4.6 Omission of Locants.

After identification of components the fusion name can be constructed. Details of how the common bonds are specified are given below. Examples are labelled, where appropriate, with the relevant letters or locants of components within the rings, and with the numbering of the whole ring system (see FR-5) outside the structure.

FR-4.1 Identification of sides of parent components

The sides around the periphery of the parent component are identified by italic letters a, b, c, etc. with a for the side 1,2; b for the side 2,3 (or in certain cases 2,2a e.g. acenaphthylene); etc. following continuously round the periphery, ignoring non-standard numbering (see Appendices 1 and 2). If there are more than twenty-six sides the additional sides are identified by subscript numbers a₁, b₁, c₁, etc. then a₂, b₂, c₂, etc. (Contrast the use of a', b', c', etc. in FR-6.1) Each letter locant implies also a direction for the specified bond, i.e. the direction of the side a is from the atom with locant 1 to the atom with the next higher locant (see arrows on the structures below).

FR-4.2 Identification of sides of attached components

The sides of attached components are identified by the appropriate pairs of number locants.

FR-4.3 Fusion of a first-order attached component to the parent component

Those bonds that are common to each component are indicated by the appropriate numerical locants for the attached components and letter locants for the parent component separated by a hyphen and cited within square brackets. Numerical locants are separated by commas, while letter locants are quoted together if there is more than one. Letter locants are cited in the same direction as they were assigned (i.e. clockwise when considered as in Appendices 1 and 2). The numerical locants are cited in the same direction as the letter locants. The first-order attached component is quoted before the locant set to which it applies and in front of the parent component name. If there is more than one first-order attached component they are quoted in alphabetical order unless second-order attached components modify this order (see FR-3.6 and FR-4.4). See FR-4.6 for the omission of locants.

Examples:

furo[2,3-g]quinoline

furo[3,2-g]quinoline

6H-pyrrolo[3,2,1-de]acridine

naphtho[2,1,8-mna]acridine

furo[3,2-g]pyrrolo[1,2-b]isoquinoline

FR-4.4 Fusion of a higher-order component to an attached component

The procedure for indicating the common bond(s) between a higher-order attached component and an attached component follows that for the attachment of the first-order attached component to the parent component (see FR-4.3) except that ony numerical locants are used instead of letters and the two sets of locants are separated by a colon. The locants of second-order attached components are primed to contrast with those of first-order attached components. The locants of third-order (fourth-order, etc.) attached components are double (triple, etc.) primed.

Example:

pyrido[1",2":1',2']imidazo[4',5':5,6]pyrazino[2,3-b]phenazine

If more than one component is fused to the same lower-order component they are cited in alphabetical order unless higher-order components alter this order (see FR-3.6).

Example:

furo[3',2':5,6]pyrano[3,2-b]imidazo[4,5-e]pyridine
(furo-pyrano before imidazo)

furo[3",2":4',5']pyrrolo[2',3':4,5]pyrano[4',3':5,6]pyrano[3,2-b]pyridine
(furo-pyrrolo before pyrano)

FR-4.5 Choice of locants

If there is a choice of numerical or letter locants (consistent with the numbering of the component) then the lower numbers or letters are selected. Preference is given in the following order:

a. Parent component letters as a set.

Examples:

furo[3,2-h]pyrrolo[3,4-a]carbazole
not furo[2,3-b]pyrrolo[3,4-i]carbazole
(a,h preferred to b,i)

6H-isoquinolino[2,1,8-mna]phenazine
not 6H-isoquinolino[8,1,2-cde]phenazine
(a,m,n preferred to c,d,e)

b. Parent component letters in order of citation.

Examples:

furo[3,4-b]thieno[2,3-e]pyrazine
not furo[3,4-e]thieno[2,3-b]pyrazine
(b...e preferred to e....b)

2H,10H-dipyrano[4,3-b:2',3'-d]pyridine
not 2H,10H-dipyrano[2,3-d:4',3'-b]pyridine
(b....d preferred to d....b)

diindeno[1,2-i:6',7',1'-mna]anthracene
not diindeno[6,7,1-mna:1',2'-i]anthracene
(i ...mna preferred to mna...i)

Note

Both names for this example have the letters a,i,m,n when compared in alphabetic order (see FR- 4.5.a), but when compared in the order of citation i ...mna is preferred to mna...i.

c. Set of locants for the first-order attached components for fusion to the parent component.

Examples:

1H-indeno[7,1-bc]azepine
not 1H-indeno[4,3-bc]azepine
(1,7 preferred to 3,4)

10H-furo[3',2':5,6]pyrido[3,4-a]carbazole
10H-furo[2',3':2,3]pyrido[5,4-a]carbazole
(3,4 preferred to 4,5)

cyclopenta[1,2-b:5,1-b']difuran
not cyclopenta[1,2-b:2,3-b']difuran
(1,1,2,5 preferred to 1,2,2,3)

2H-tripyrano[4,3,2-de:4',3'-g:3",4",5"-ij]phthalazin
not 2H-tripyrano[3,4,5-de:3',4'-g:2",3",4"-ij]phthalazin
(2,3,3',3",4,4',4",5" preferred to 2",3,3',3",4,4',4",5)

d. First-order attached component locants for fusion to the parent component in order of citation.

Example:

pyrazolo[4',3':6,7]oxepino[4,5-b]indole
not pyrazolo[3',4':2,3]oxepino[5,4-b]indole
(4,5 preferred to 5,4)

e. Locants for lower-order attached components as a set for fusion to higher-order attached components.

Examples:

pyrano[3',2':4,5]cyclohepta[1,2-d]oxepine
not pyrano[2',3':5,6]cyclohepta[1,2-d]oxepine
(4,5 preferred to 5,6)

cyclopenta[6,7]furo[3',2':3,4]cycloocta[1,2-c]pyrrole
not cyclopenta[4,5]furo[2',3':7,8]cycloocta[1,2-c]pyrrole
(3,4,6,7 preferred to 4,5,7,8)

difuro[2",3":3',4';2"',3"':5',6']cyclohepta[1',2':5,6]cycloocta[1,2-c]pyrole
not difuro[3",2":4',5';3"',2"':6',7']cyclohepta[1',2':5,6]cycloocta[1,2-c]pyrole
(3',4',5',6' preferred to 4',5',6',7')

f. Locants for lower-order attached components for fusion to higher-order attached components in order of citation.

Example:

pyrrolo[3',2':4,5]cyclohepta[1,2-b]quinoline
not pyrrolo[2',3':5,4]cyclohepta[1,2-b]quinoline
(4,5 preferred to 5,4)

g. Locants for higher-order attached components as a set for fusion to the lower-order attached component.

Example:

7H-indeno[7',1':5,6,7]cycloocta[1,2,3-de]quinoline
not 7H-indeno[3',4':5,6,7]cycloocta[1,2,3-de]quinoline
(1',7' preferred to 3',4')

h. Locants for higher-order components for fusion to lower-order components in order of citation.

Example:

pyrano[2",3":6',7']thiepino[4',5':4,5]furo[3,2-c]pyrazole
not pyrano[3",2":2',3']thiepino[5',4':4,5]furo[3,2-c]pyrazole
(4',5' preferred to 5',4')

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