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Nodal NomenclatureЦGeneral Principles.

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Volume 18 . Number 12
December 1 9 7 9
Pages 887-966
International Edition in English
Nodal Nomenclature-General
Principles
By Noel Lozac'h, Alan L. Goodson, and Warren H.
A new, comprehensive graph-based nomenclature system for chemical substances is proposed.
Substances are named by using nodal nomenclature to name graphs derived from their structures by ignoring chemical details such as atom identities, bonding, charges, etc. After the fundamental graph is named, these chemical details are introduced by modifications and additions
to the name of the graph to yield the name of the actual substance. Although development of
nodal nomenclature originated with problems in naming some organic systems, it is not limited
to organic substances. In this paper, only general principles for naming the graph are described applications to specific substances will be discussed in future papers.
1. Preface
The work reported here originated as a suggestion by one
of us (N. L.) during the 1973 meeting of the Commission on
the Nomenclature of Organic Chemistry (CNOC) of the International Union of Pure and Applied Chemistry (IUPAC).
It soon became apparent that this concept, conceived as a basis for naming a class of compounds known as "cyclophanes", had a very much wider applicability. In fact, its potential surpasses the confines of organic chemistry.
Independently, as part of a continuous review of nomenclature procedures, a study of ring nomenclature was started
at Chemical Abstracts Service (CAS) in 1972 which developed into an effort to produce a general, graph-based nomenclature system.
When, at the 1975 meeting of CNOC, it became apparent
that the CAS work and nodal nomenclature were developing
['I
Prof. N . Lozac'h ['I
Institut des Sciences de la Matiere et du Rayonnement
Universite de Caen
14032 Caen Cedex (France)
Dr. A. L. Goodson and Dr. W. H. Powell
Chemical Abstracts Service
P.O. Box 3012
Columbus. Ohio 43210 (USA)
[ '1 To whom correspondence should be addressed.
Angew. Chem. lnt. Ed. Engl. 18, 887-899 (1979)
along very similar lines, the evaluation and further development of nodal nomenclature became a joint effort.
Chemical nomenclature has developed in a rather random
manner, paralleling the development of chemistry. Its principles were therefore not conceived from the beginning with a
clear, overall plan, resulting in a mixture of nomenclature
systems with overlapping rules, inconsistencies, and inadequate treatment for some types of compounds. An extensive
set of organic nomenclature rules has been published['-41,
which is primarily a codification of the practices used by the
chemical community insofar as these practices were determined to be sound.
The main objective of CNOC now is to improve this existing system of organic nomenclature. Accordingly, CNOC is
engaged in revising its rules mainly through simplification,
systematization, and extension, as necessary, and plans to
publish these revised rules['].
Nodal nomenclature will not be included in the proposed
revised rules because to do so would not conform to the established CNOC policy of recommending the codified use of
existing nomenclature practices. However, the potential of
the nodal nomenclature system has been recognized and
CNOC has therefore encouraged the publication of its basic
principles and some guidelines for its use. This will enable
nodal nomenclature to be used and evaluated by the chemi-
0 Verlag Chemie, GmbH, 6940 Weinheim, 1979
0570-0833/79/1212-0xX7
$ 02.50/0
887
cal community where current nomenclature systems prove
difficult, cumbersome, or inadequate. The experience gained
will provide constructive criticism and guidance for further
development. We do not regard nodal nomenclature as fully
developed at this time and anticipate that some minor modifications may be necessary or desirable before i t is considered
by CNOC for assimilation into the IUPAC system of organic
nomenclature.
We have taken considerable care to ensure that nodal
nomenclature is compatible with existing nomenclature systems as well as with the proposed revised rules in order that
nodal nomenclature will be as widely applicable as possible.
Thus, some of the traditional practices of present nomenclature systems need not be abandoned.
One of the most important features of nodal nomenclature
is that this is the first time a comprehensive, computer-compatible system has been introduced to name structure graphs
systematically, although numerous papers have been published dealing with structure graphs as an aid to describing
ring systems. Furthermore, the resulting names are easily
modified to describe actual chemical substances.
Complex examples with long systematic names are used at
times in this paper to demonstrate the wide scope and facile
application of nodal nomenclature, but it must be emphasized that nodal nomenclature has not been developed solely
for naming unusual or complex structures; it is a system with
completely general applicability. Structures which can be
named easily by traditional nomenclature systems can be
named just as easily by nodal nomenclature with attendant
supplementary advantages.
2. Introduction
Development of nodal nomenclature was prompted by the
recognition of various shortcomings in existing organic nomenclature systems. Most of these deficiencies are related in
one way or another to the fact that even relatively simple
structures, such as hydrocarbons, must be often described by
substitutive principles, for example:
7H3
CH3CH2CHCH2CH3
3 -Methylpentane
@ELH3
2 - Phenylpropane
or
Isopropglbenzene
Consequences of using the substitutive principles of existing organic nomenclature systems include: (a) the names of
simple structures, such as those illustrated above, are obscured and often completely lost when the structures are substituted by characteristic groups; (b) multiple occurrences of
characteristic groups are often scattered throughout the
name; and (c) unique locants are not available to denote
each skeletal atom in the structure. These problems are illustrated in the following derivatives of the hydrocarbons
shown above.
These problems are sometimes avoided in traditional organic nomenclature by use of a number of trivial names, i. e.
simple names implying relatively large structural units,
usually with complete unique numberings and often with im888
3-(Chloromethyl)1,s-pentanediol
1,l-Dichloro- Z(4-nitropheny1)propane
or
1-(2 , 2 - D i c h l o r o - 1 - m e t h y l
ethyl) 4-n i t r obenzene
~
CHzOH
I
ClCHZCHzCHCH,CH2C1
c1
4-C h l o r o - 2- ( 2 - c h l o r o ethyl). 1 - b u t a n o l
3 - ( 2 -C a r b o x y - 5 - c h l o r o phenyl) - 2 - c h l o r o - 2 pentenedioic a c i d
FHzCOzH
Q
\ C=CCICOzH
COzH
plied stereochemistry. Such trivial names coexist with systematic names which are usually longer because they are derived from smaller structural units. The examples below illustrate this situation.
Phenothiazine
or
1OH-Dibenzo[b,e][ 1 , 4 I t h i a z i n e
H02C\
c,
H
Maleic acid
or
cis - B u t e n e d i o i c a c i d
,COzH
=c\
H
H02C-CHOH-CHOH-C
OzH
T a r t a r i c acid
or
2,3 - D i h y d r o x y b u t a n e d i o i c a c i d
Nodal nomenclature describes the graph of a compound
and avoids the deficiencies noted above by providing a
unique locant for each position in the structure (see Section
3). However, even though substitutive principles need not be
used to describe the graph of a substance, as is the case in
traditional systems, they may be used to indicate characteristic groups in names for specific compounds. This will be discussed in later papers.
3. General Concepts of Nodal Nomenclature
The basic logic of nodal nomenclature resides in the description of a structure in terms of its graph. The term
“node’’[61is derived from the Latin “nodus” and has the
meaning of a knot, bulge, or intersection of branches. It is
applied to single skeletal units, i. e., atoms, of a structure. It
may also be applied to groups of atoms forming important
structural units, such as a benzene ring in a cyclophane, an
amino acid fragment in a polypeptide, or a mononuclear
component of a polynuclear acid. Nodes representing such
groups of atoms can be called “contraction nodes”.
General nodal nomenclature, the subject of this paper, describes the numbering and arrangements of nodes of a graph.
It does not specify the nature of the nodes. Specific nodal
nomenclature, on the other hand, describes the nature or
structure of the nodes, specifies the bonding between the
nodes, etc. It will be discussed in subsequent publications.
Since the graph concept for naming and numbering[*’
structures is most easily illustrated by use of graphs derived
[*] Here “numbering” means the assignment of locants to nodes or skeletal
atoms (and of module seniority numbers to module seniority descriptors).
Angew. Chem. Int. Ed. Engl. 18, 887-899 (1979)
from organic structures, the rules of general nodal nomenclature are often illustrated in this paper by graphs derived from
hydrocarbons and heterocycles. In addition, we use the suffix
“-ane” (as “nodane”) which denotes saturated structures in
traditional organic nomenclature. However, this should not
be taken to imply in any way that nodal nomenclature is not
equally applicable to other types of compounds, such as
coordination compounds. Furthermore, the examples and
terminology of this paper should not conceal a fundamental
difference between the concepts of classical organic nomenclature and those of nodal nomenclature. In classical organic
nomenclature, the skeletal atoms are usually atoms of the
common nonmetallic elements (such as carbon, nitrogen,
and oxygen) and have defined ligancies based on classical
valence considerations. On the other hand, in general nodal
nomenclature, the ligancy of a node is not limited in any way
and therefore a node can have a ligancy of any value, which
becomes apparent only when the nature of the node is defined.
In contrast to classical organic nomenclature, nodal nomenclature provides a unique numerical locant for every
node of a graph. This may also be useful in some specialized
areas of traditional organic nomenclature, such as steroids
and alkaloids, where trivial names may be preferred to systematic ones. Although proliferation of trivial names is not desirable, they are simpler than systematic organic names and
often imply considerable stereochemical information. One
rather serious problem with many trivial names is that the associated numbering is sometimes incomplete, often arbitrary,
and may vary from structure to structure within the same
class. Nodal nomenclature, on the other hand, provides a
general numbering system that can be used with any trivial
name or nomenclature system.
Before any specific compound can be named by nodal
nomenclature, two decisions dealing with its structure need
to be made. First, the parts of the structure that are to be excluded from the portion of the structure to which general nodal nomenclature is to be applied-and are therefore to be
treated as substituents-must be determined. This choice is
not necessary in the most general application of nodal nomenclature, but is peculiar to classical organic nomenclature.
It is included here because, as noted above, we want to make
general nodal nomenclature as compatible as possible with
existing nomenclature systems (see Section 1). Secondly, the
nature of the nodes that will be named by nodal nomenclature must be determined. General nodal nomenclature does
not define the nature of the nodes; this is dependent on the
type of compound and the circumstances in which it is reported. However, in order to name the graph by the principles of general nodal nomenclature, it is necessary to define
the nature of the individual nodes. For example, the structure shown below can be named on the basis of graph A (in
which each node is an atom) or of graph B (in which each
pyridine ring has been “contracted” to a single node (con-
F N
-
A
Angew. Chem. Ini. Ed. Engl. 18, 887-899 (1979)
B
traction node) to simplify the graph, as has been proposed
for naming cyclophanes)[71.
Once the graph has been defined, general nodal nomenclature is used to describe the arrangement and numbering
of the nodes, as detailed in this paper. Then, as will be discussed in subsequent papers, specific nodal nomenclature is
used to describe the nodes, bonding, and substituents expressed as prefixes and/or suffixes.
Only after the nodes and bonds of the graph have been
specified are the ligancies of the nodes satisfied by attaching
hydrogen as needed if substitutive nomenclature is to be used.
Thus, in general nodal nomenclature the graph of 3-methylpentane (see Section 2) would be named [5.I3]hexanodane.
In specific (substitutive) nodal nomenclature this parent hydrocarbon could be named, according to the rules of Section
G”], as [5.1’Ihexacarbane, or, more traditionally, as
[5.13]hexane.The silicon analog could be named [5.13]hexasilane. Such parent hydrides can be substituted by characteristic groups as in classical organic nomenclature to yield
names such as 5,6-dichloro[5.1’]hexacarban-l-ol; according
to current rules the compound has the name 5-chloro-3(chloromethy1)-I-pentanol.
It is evident from the preceding discussion that, in comparison with classical organic nomenclature, nodal nomenclature has many advantages, including:
1. consistent treatment of chains and rings, and of assemblies of chains and rings;
2. systematic numbering of the atoms in complex structures,
as commonly occur in natural products, such numberings
being equally applicable to structures described by trivial
or semisystematic names;
3. applicability to structures with nodes of high ligancy as,
for example, occur in coordination compounds;
4. logical description of an assembly of subunits or modules
of any type or degree of complexity, such as: (a) cyclic systems in ring assemblies, protophanes and cyclophanes; (b)
amino acid fragments in polypeptides and proteins; (c)
mononuclear components in polynuclear acids;
5. the nomenclature is suitable for computerization.
4. Glossary
For the usual terms of classical organic nomenclature, the
definitions given in References I’ 41 are followed. In addition,
there are certain terms used in this and subsequent papers in
this series which have a new or special meaning. These terms
are defined as follows:
General Nodal Nomenclature: The description and numbering of the arrangement of
nodes in a graph.
Assembly (of modules):
A structure graph composed
of more than one cyclic module or of at least one acyclic
module and at least one cyclic module.
Contraction (of a module):
The operation by which a
module is reduced to a contraction node to simplify the
descriptor and name a structure or to facilitate the numbering.
889
Contraction node:
A group of nodes, that can
be named as a unit in specific
nodal
nomenclature,
which is contracted to a single node to facilitate the description of a complex system in general nodal nomenclature.
Structure Graph
(see Graph):
Descriptor:
The numeric portion of a nodal name[*], enclosed in
brackets,
providing
an
unambiguous description of
a graph.
5. Proposed Rules for General Nodal Nomenclature
Graph (Structure Graph):
An arrangement of nodes
and lines representing, respectively, the atoms or
groups of atoms and bonds
(or connectivities) forming a
molecule.
Module:
A single node or an entirely
cyclic or acyclic subset of
nodes that is treated as a separate entity during the numbering and naming of a
graph assembly.
Module Seniority Descriptor
A capital letter assigned
to each module to designate
its relative seniority in an
assembly of modules.
Module Seniority Graph
An arrangement of module
seniority descriptors used for
determining the order in
which the various modules
of an assembly are to be
numbered.
Module Seniority Number
Arabic numeral assigned to a
module seniority descriptor
in a module seniority graph.
Nodef6]:
The simplest unit of a graph,
representing either a single
atom or a group of atoms.
Principal Module:
The senior module where
numbering of the module seniority graph and unique
numbering of the corresponding assembly begins.
Senior Module:
The module, or one of the
modules, of highest seniority
in an assembly.
Specific Nodal Nomenclature: The description and numbering of a chemical structure, the specific nodal name
being obtained by adding to
the general nodal name a description of such details as
the nature of the nodes,
bonding, charges, etc.
890
Used principally to ensure
that graphs related to chemical structures are not confused with other types of
graph, e. g., graphs related to
reaction sequences.
Rule N-1-Acyclic Graphs
N-1.1. A n acyclic graph is an unbranched chain of nodes or
two or more unbranched chains of nodes connected to each
other without formation of a cyclic structure. No matter how
complex, it is never considered as a combination of separate
structural
N-1.2. The main chain in an acyclic graph is the longest
unbranched chain of nodes and is numbered first, from one
end to the other. When an acyclic graph has two or more
equal unbranched chains of greatest length, the main chain
is the one having the longest branches (see Rule N-1.3) attached to it. The main chain is numbered so that the lowest
possible locants are given to these longest branches. If a
choice remains, see Rule N-1.6.
N-1.3. Branches in an acyclic graph are unbranched chains
of nodes attached to the main chain or to other, longer
branches. Each is numbered from one end to the other, beginning always with the node attached to the part of the
graph already numbered.
N-1.4. Branches in an acyclic graph are numbered successively in order of decreasing length. When two or more
branches are of equal length, they are numbered in increasing order of the locants already assigned for the nodes of the
chain(s) to which they are attached.
N-1.5. The descriptor of an acyclic graph consists of square
brackets enclosing: (a) an Arabic numeral indicating the
number of nodes in the main chain; (b) a period, followed by
Arabic numerals denoting the number of nodes in each
branch, cited in the order of their numbering (see Rule N1.4); and (c) a superscript locant for each branch numeral denoting the node of the part of the graph already numbered to
which the branch is attached“’!
N-1.6. When two or more alternative descriptors for an
acyclic graph can be derived, the correct descriptor is the one
having the lowest superscript number at the first point of difference when these locants are compared term by term from
the beginning of the descriptor[”l.
N-1.7. The name of an acyclic graph consists of: (a) the descriptor derived as in Rule N-1.5 (b) a multiplying prefix,
such as “di-”, “tri-”, “tetra-”, etc.[‘*I,denoting the total number of nodes; and (c) the ending “ - n ~ d a n e ” [ ’ ~ ~ .
I
1.
=
-6
[ 61Hexanodane
2’
T
[5.13]Hexanodane
Angew. Chem. I n t . Ed. Engl. 18, 887-899 (1979)
3.
12
I1
[ 10.l2l7l8]Tridecanodane
II
10
13
17
I6
[9.24141418181a1a]Heptadecan~dane
4'
w
[ 9.3415ITridecanodane
[ 11.3525292915151g19]Tetracosan~dane
-
Rule N-2.--Monocyclic Graph
I
5.
19
?O
[ 13.5725114115]Do~osan~dane
14
[ 8 . 34251121Tetradecanodane
&
-/
7.
I7
N-2.1. Monocyclic graphs are numbered sequentially from
any node in either direction until all nodes are numbered.
N-2.2. The descriptor of a monocyclic graph consists of
square brackets enclosing a zero (indicating the presence of a
ring) and an Arabic numeral denoting the number of nodes
forming the ring.
N-2.3. The name of a monocyclic graph consists of: (a) the
descriptive prefix "cyclo"; (b) a descriptor derived according
to Rule N-2.2 (c) a multiplying prefix indicating the number
and (d) the ending "-n~dane"['~'.
of nodes in the
Example:
a
= $
~
I6
20
21
Cyclo[ 08Joctanodane
1" 1'4114]Henicosanodane
[ 10.35351
'
Rule N-3.-Polycycfic Graphs"'
[ 13.67672315
1'1"
I8
9.
115 1'7121 lZ3]Tetratriacontanodane
10
* = =
[ 1 2.5635213121]Tri~osan~dane
21
20
[ 1 2.4631329114118]Tri~o~an~dane
Note: The descriptor [12.463'3291'51'7]is not correct because the locant series 6,13,9,15,17 is higher than 6,13,9,14,18
(Rule N-1.6).
Angew. Chem. inr. Ed. Engl. 18, 887-899 (1979)
N-3.1. A polycyclic graph consists of a monocyclic ring of
nodes and one or more bridges, which are valence bonds or
chains of nodes connecting nodes of the main ring and/or
other bridges in the polycyclic system.
N-3.2. The main ring in a polycyclic graph is the monocyclic ring containing the greatest number of nodes. When two
or more monocyclic rings have the same number of nodes,
the main ring is chosen according to Rule N-3.6.
N-3.3. The main bridge in a polycyclic graph is the longest
unbranched chain of nodes both ends of which are attached
to the main ring"']. When two or more chains are of equal
length, the main bridge is chosen according to Rule N-3.6.
Other bridges are called secondary bridges.
N-3.4. The numbering of a polycyclic graph begins at one
of the nodes of the main ring to which the main bridge is attached (bridgehead) and proceeds in the direction that gives
the lower locant to the other bridgehead. The main bridge is
numbered sequentially after the main ring, beginning with
the node of the main bridge connected to the node in the
main ring having the locant 1. The secondary bridges are
numbered successively in the same manner, beginning always with the longest bridge (or one of the longest bridges)
connected to nodes of the graph previously numberedl"].
When there is a choice between two or more bridges of the
same length, the first to be numbered is the one attached to
['I
In nodal nomenclature phanes can be treated as mono- or polycycles
891
the node having the lowest locant in the part of the graph
previously numbered. Each bridge is numbered beginning
with the node of the bridge connected to the node of the part
of the graph previously numbered having the lower locant.
N-3.5. The descrQtor of a polycyclic graph consists of
square brackets enclosing: (a) a zero indicating the presence
of a ring followed by an Arabic numeral indicating the number of nodes in the main ring (see Rule N-2.2); (b) a period
followed by Arabic numerals denoting the number of nodes
in each bridge, cited in the order of their numbering (see
Rule N-3.4); and (c) a pair of superscript locants for each
bridge numeral, separated by a comma and cited in increasing numerical order, denoting the nodes in the part of the
polycyclic graph already numbered to which each bridge is
attached['*l.
N-3.6. When two or more alternative descriptors for a polycyclic graph can be derived because there is a choice for the
main ring, main bridge, starting point and/or direction of
numbering, Arabic numerals, in each descriptor, denoting
the lengths of the bridges and the positions of the bridges in
the graph are compared term by term in the order they appear (see Rule N-3.5). The correct descriptor is the one with
the preferred Arabic numeral at the first difference: if the
first difference corresponds to a bridge length, the preferred
numeral is higher; if the first difference appears in a superscript numeral (locant), the preferred numeral is lower[19J.
N-3.7. The name of a polycyclic graph consists of: (a) a descriptive prefix, such as "bicyclo-", "tricyclo-", etc., indicating the number of rings in the ring system['']; (b) the descriptor derived according to Rules N-3.5 and N-3.6 (c) a multiplying prefix1121
indicating the total number of nodes; and
(d) the ending "-n~dane"['~].
Examples1211:
1.
V
Tricyclo[O9. 1"501'5]decanodane
"(4.3.1 ~ ~ r o p e ~ a n e
8.
Tricycle[ 08. 11'513'7]decanodane
9.
"Adamantane
10.
Tricyclo[09.21'511'6]dodecanodane
11.
T e t r a c y c l o [ 0 10. 11'4Z'''11
tridecanodane
4
T e t r a c y c l o [ 010.3''' 13*504'8].
tetradecanodane
12.
,.
1
T e t r a c y c l o [ 010. 1lf5168'003a8]dodecanodane
*Iceane
13.
Pentacyclo[08.0"402""05's]octanodane
"Cubane
14.
Bicyclo[ 0 5. 4'j' Inonanodane
a
BicycloL 07. 1"4]octanodane
I
15.
4
0
9 1
4
Note: The descriptor [07.1'.5]is not correct because, for the
main bridge, the locant series 1,5 is higher then 1,4 (Rule N3.4).
Pentacyclo( o 12. 0"603~1004~907~'21dodecanodane
"Tetraasterane
3
~ e n t a c y c l oo(12. 11,4513,13
1.7J041g,'
tricosanodane
16.
17.
:@:
I
Hexacyclo( 07. 0"30'~401~501'602'7]heptanodane
Tricycle[ 06.41r'44441t e t r a d e c a n o d a n e
5.
7
6
14
Tricycle[ 06 .31"48'8]tridecanodane
6.
9
892
1-
Bicyclo[O6. 21'4Joctanodane
6@
3.
05"
Hexacyclo(05. 21"22'223,324'425'51pentadecanodane
"(5lRotane
I3
Angew. Chem. Int. Ed. Engl. 18, 887-899 (1979)
Rule N-4.-Assernblies of Cyclic and Acyclic Graphs
N4.1. A structure graph is called an assembly if it is composed of more than one cyclic module or of at least one acyclic module and at least one cyclic module['].
Examples:
t
N-4.11. An acyclic moduie is a single node or a branched or
unbranched chain of nodes in an assembly.
N-4.12. A cyclic module is the graph of a ring or ring system in the conventional meaning of these terms[". Assemblies of directly-connected, identical cyclic modules, such as
the structure graph of terphenyl, are not considered as one
module; each component is considered as a separate cyclic
module.
N-4.2. An assembly descriptor consists of square brackets
enclosing: (a) in parentheses, the nodal descriptor of the
principal module (which is the senior module (determined
by Rule N-4.3), or one of the senior modules, chosen according to Rules N-5.34 and N-5.4); (b) in parentheses, the nodal
descriptors of the remaining modules, cited in order of numbering according to Rules N-5.3 and N-5.4r22i;
and (c) numerical locants, separated by colons, indicating the nodes
through which each pair of modules is linked, each locant set
linking the appropriate pair of module descriptors.
Example: [(06)1:7(4)10: ll(05)l
N-4.21. The descriptor of each module in an assembly is
identical with the descriptor of the corresponding isolated
graph except that the enclosing square brackets are replaced
by parentheses. Accordingly, this descriptor retains its original numbering, i. e., the numbering that would be used to describe it if it were an isolated graph.
Example: [(06.11.4)2:10(4.12)]
N-4.22. The locant set separating each pair of module descriptors in an assembly descriptor is derived from the definitive sequential numbering for the whole assembly as given in
Rule N-5. Each locant set is written as follows: (a) the locant
of the node, in the part of the graph previously numbered,
through which the following module is attached (b) a colon;
and (c) the locant of the node, in the following module,
through which that module is attached to the part of the
graph previously numbered.
Example: [(06.11.4)2:10(4.12)]
N-4.23. In an unbranched assembly with a terminal principal module, the first locant of any locant set refers to the immediately preceding module. Each locant is higher than the
immediately preceding locant in the descriptor.
Example: [(06)1: 7(06)10: 13(06)16: 19(06)]
Note: The locant series 1,7,10,13,16,19increases steadily.
N-4.24. In an unbranched assembly with a nonterminal
principal module and in a branched assembly, the first locant
of at least one locant set refers to a module cited in the descriptor earlier than the immediately preceding module. This
Angew. Chem. Int. Ed. Engl. 18,887-899 (1979)
locant is lower than the immediately preceding locant in the
descriptor.
Examples:
1. [(06)1:7(05)4: 12(05)]
Note: In this descriptor of an assembly with a nonterminal
principal module, the locant series 1,7,4,12 does not increase steadily and the locant 4, being lower than 7, refers
to the first module cited in the descriptor, and not to the
second module.
2. [(06)1:7(06)9: 13(06)11: 19(06)]
Note: In this descriptor of a branched assembly, the locant
series 1,7,9,13,11,19does not increase steadily and the locant l l , being lower than 13, refers to the second module
in the descriptor, and not to the third module.
N-4.3. Seniority of modules in an assembly is determined
by the following criteria, which are applied successively until
a decision is reached["]:
a) Largest number of nodes.
b) Cyclic module preferred to acyclic module.
c) Largest number of rings or branches (side chains).
d) Largest main ring or longest chain.
e) Longest bridge or branch (side chain).
f) Lowest locants for attachment of bridges or branches (side
chains).
Examples (in order of decreasing seniority: the criterion deciding the seniority of an example over the one following is
noted in each case):
Tricycle[ 01 1. 1"408'12]dodecanodane
1.
(senior to the following module, according to criterion a)
2.
'ye
[7.3413]Undecanodane
I1
8
ID
(senior to the following module, according to criterion e)
(senior to the following module, according to criterion a)
(senior to the following module, according to criterion e)
(senior to the following module, according to criterion c)
6.
#
Bicyclo[ 08.1"4]nonanodane
4
(senior to the following module, according to criterion f )
893
Bicycle[ 08.1"5]nonanodane
7.
(senior to the following module, according to criterion a)
ding to each of its original locants a number equal to the total number of nodes in the assembly that have already been
assigned definitive locants. When there is a choice for the
origin and/or the direction of numbering in a module, the
correct numbering is the one giving the lowest locants to the
nodes of attachment of the module to other modules in the
assembly.
Example:
Bicycle[ 08.0"5]octanodane
8.
(senior to the following module, according to criterion d)
9.
el
A
Bicyclo(07. 11'3]octanodane
(senior to the following module, according to criterion b)
10.
'
=
z
=
=
=
=
i
B
This assembly consists of two modules, A and B. The procedure for numbering this assembly is:
a) Module A, the senior module of the assembly (see Rule N4.3a), is numbered and the descriptor generated according
to Rule N-3.
[ 810ctanodane
(senior to the following module, according to criterion a)
11.
'w
6
[5. 1213]Heptanodane
7
(senior to the following module, according to criterion c)
12.
[6.12]Heptanodane
I
(senior to the following module, according to criterion f )
(senior to the following module, according to criterion d)
14.
Since this module is the principal module of the assembly
(see Rule N-4.2), it retains this numbering in the final
numbering of the assembly. However, in this module
there are two possible origins for numbering, each with
two possible directions. Hence, in the assembly, the module is numbered so that the locant for the node of the attachment to the next module is as low as possible, i. e., 2
(not 3, 5 or 6).
Module B is numbered and the descriptor generated according to Rule N-1.
Module B is renumbered by adding 7 (the total number of
nodes in module A) to each original locant.
'y
.
i
[5.Z3]Heptanodane
7
N 4 . 4 . The name of an assembly consists of: (a) a descriptive prefix (such as "cyclo", "bicyclo", etc.) indicating the total number of rings in the assembly; (b) the assembly descriptor (see Rule N-4.2);(c) a multiplying prefix['*]indicating the
total number of nodes in the assembly; and (d) the ending
LL-n~dane"['31.
Example: Bicyclo[(06) 1 :7(05)4 :13(3)] tetradecanodane
Rule N-5.-Definitive Numbering of Assemblies
N-5.1. The definitive numbering of an assembly defines the
correct assembly descriptor. This numbering begins with the
principal module (see Rule N-4.2) for which the original
numbering is retained. The other modules are renumbered
sequentially, beginning with a module adjoining the principal module and proceeding, where necessary, as described in
Rules N-5.3 and N-5.4.Each module is renumbered by ad-
894
d) The modules are recombined with their new numberings,
where needed, and named according to Rule N-4.4.
All
Bicycle[ ( 06.1lP4)2: 1O(4. 12)]dodecanodane
N-5.11. All assemblies in which the principal module terminates a single linear chain of modules are numbered and
named by extension of the procedure described in Rule N5.1.
Example:
Bicyclo[(O6)1: 7 ( 4 ) 1 0 : ll(05)lpentadecanodane
Angew. Chem. Inl. Ed. Engl. 18,887-899 (1979)
N-5.12. In assemblies in which the principal module is attached to a single, branched chain of modules or to two or
more linear or branched chains of modules and in which two
or more definitive numberings are possible, the correct numbering is chosen on the basis of the order of module seniority
numbers assigned to the module seniority descriptors of the
module seniority graph (see Rules N-5.2 and N-5.3). When
this is not definitive, the correct numbering is chosen by
comparing the descriptors derived from the various possible
numberings (see Rule N-5.4).
N-5.2. The module seniority graph of an assembly is a representation of the component modules of the assembly in
terms of their relative seniorities. Each component module is
represented in the module seniority graph by a capital letter,
i.e. a module seniority descriptor, signifying its relative seniority and its position in the assembly. The most senior
module(s) is (are) denoted by A, the next most senior by B
etc.
Example:
first assigned to the unbranched chain in which the most senior contraction node is encountered at the first difference,
the module seniority descriptors being compared term by
term in order of seniority as defined in Rule N-4.3, regardless
of their positions in the chain, and then in order of their position in the chain.
Examples:
I
1.
h
Y
q-D-E
I
A-B-C-D-E-B
1
2
7
4
6
7
( B D E h a s p r e f e r e n c e over C D E )
5
6
D-B
2.
A-?-~-B-D
1
-
3
(BD has preference over DB)
4
)
N-5.314. Branches to the main chain of contraction nodes
are numbered according to the following criteria which are
applied successively as far as necessary in order to achieve a
definitive numbering: (a) in order of decreasing length; (b) in
order of seniority of the module seniority descriptors as defined in Rule N-5.313; (c) in order of the increasing numerical value of the seniority number for the contraction node to
which the branch is attached in the part of the chain already
numbered.
Examples:
fr
7
00-
Module:
Contraction
node:
A
B
C
14
D
D-B-A-C-B
?-G-B-F
N-5.312. In a branched module seniority graph, the longest
unbranched chain of module seniority descriptors (the main
chain) is numbered first according to Rule N-5.311, followed
by the branches attached to the main chain, in order of decreasing seniority as given in Rule N-5.313, where necessary.
Example:
B
I
3
4
N-5.313. When, in a branched module seniority graph, two
or more chains are of equal length, seniority numbers are
Angew. Chem. In(. Ed. Engl. 18,887-899 (1979)
I
A-B-C-B-D
2.
I
N-5.3. Numbering of the module seniority graph, i. e. assignment of the module seniority numbers, which determines the
order of assignment of the definitive sequential numbering
of the assembly (see Rule N-5.1), begins with the principal
module (see Rule N4.2) and proceeds, in order of decreasing
seniority as defined in Rule N-5.33, through each chain of
contraction nodes attached to the principal module'23'.
N-5.31. Module seniority numbers are assigned to each
chain of contraction nodes attached to the principal module
of the seniority graph.
N-5.311. An unbranched chain of contraction nodes is
numbered sequentially after the principal module whose
seniority number is 1, according to Rule N-5.1.
Example:
2
+-B-~-B-F-E
1.
A
seniority
graph:
I
9
6
Module
A-E-C-D
8
€f-D-E
I
1
4
13
1
8
9
D
D
D
4
5
I
l
A-B-B-C-B-B
3.
I
2
5
3
l
6
N-5.315. Branched branches of contraction nodes are numbered by following the procedures given in Rules N-5.312
and N-5313.
N-5.32. When two or more chains of contraction nodes
are attached to the principal module, module seniority
numbers are assigned to each chain in its entirety, as described in Rule N-531, before proceeding to the next.
Example:
Y--B-A-?-C
4
1
.
3
not
C-B-A-B-C
4
,
1
C-B-A-V-C
not
2
5
5
1
1
-
N-5.33. Module seniority numbers are assigned to two or
more chains of contraction nodes attached to the principal
module in order of seniority according to the following criteria, considered successively until a definitive numbering is
obtained:
a) Largest number of contraction nodes in the entire chain.
Example:
E-F-G-D-A-B-C
5
4
3
2
eI
1
6
7
b) Longest unbranched chain of contraction nodes.
Example:
I5
D-E-E-A-C-B
4
3
2
I
1
1
6
895
4
c) The most senior contraction node encountered at the first
difference, the module seniority descriptors being compared term by term in order of seniority as defined in
Rule N-4.3, regardless of their positions in each chain.
Example:
D-B-A-C-B
5
4
1
2
(BC
1
not BD)
N-5.4. When a definitive order for numbering the modules
of an assembly cannot be determined by sole application of
the principles of the module seniority graph (Rules N-5.2
and N-5.3)[**',the correct order corresponds to the assembly
descriptor that has the lowest locants defining the attachments of the modules. The set of lowest locants is the locant
series having the lowest locant at the first point of difference
when two or more series are compared term by term in order
of appearance in each assembly descriptor.
Examples:
d) The most senior contraction node having the lowest seniority number
Example:
not
B-C-A-B-C
5
4
1
2
B-C-A-B-C
3
3
2
1
4
5
(BC nof CB,because 2 is lower than 3)
N-5.34. When a module seniority graph contains two or
more modules of highest seniority, i. e. with module seniority
descriptor = A, theprincipal module is that senior module to
which is attached the most senior chain of contraction nodes,
as determined by the criteria described in Rule N-5.33.
Examples:
not
A-A-B
1
2
3
1.
1
Note: The descriptor [(06.1 1,4)2:8(06.1 '*")I is not correct
because the locant series for the module attachments 2,8 is
higher than 1,9.
3
4
4
A
A
not
A-A-A
1
2
I
A-?-A
I
2
3
2.
( s e e Rule N-533a)
8
5
D
D
I
C-B-A-A-B-C-D
7
6
1
2
1
4
5
not
13
Tetracyclo[(OG. 1104)1: 9(06. 11'4)]
tetradecanodane
A-A-B
2
Q
. &#
x
( s e e R u l e N-5.33a)
I
25
19
T e t r a c y c l o [ ( O 6 ) 1 : 7(2)8 : 9(06)12 : 1 5 ( 0 5 ) 1 7 : 20(1)7 : 21(05)]pentacosanodane
I1
I
C-B-A-+-P-C-D
4
3
2
1
12
T r i c y c l o [ ( O 6 ) 1 : 7(05)8 : 1 2 ( 2 ) 4 : 1 4 ( 0 5 ) 1 6 : 1 9 ( 2 ) ]
icosanodane
8
( s e e R u l e N-5.33b)
D-A-B-A--C
5
1
1
3
(ABAC, not
6
5
4
4
D-A-B-A-C
4
3
2
1
Note: The descriptor [(06)1:7(05)9: 12(2)4:14(05)15: 19(2)]
for this assembly, whose seniority graph is C-B-A-B-C, is not
correct because the locant series 1,7,9,12,4,14,15,19 is higher
than 1,7,8,12,4,14,16,19.
5
ABAD, s e e R u l e N - 5 . 3 3 ~ )
C-A-D-B-B-A-C
( B B , not
not
1
2
1
1
nof
C-A-D-B-B-A-C
7
1
2
1
4
5
6
DB, s e e R u l e N-5.33d)
N-5.35. When the numbering of the module seniority graph
is defined unambiguously by Rules N-5.31 through N-5.34,
an assembly is numbered by the procedure of Rule N-5.1 applied to the modules in order of increasing numerical value
of their seniority numbers.
Example (see the assembly illustrating Rule N-5.2
above):
D-B-A-c-B
S
4
1
-
Note: The descriptor [(06)1:7(3)9: 10(06)13:16(05)18:
21(1)4: 22(05)23 :27(1)] for this assembly, whose seniority
graph is D-B-A-C-A-B-D, is not correct because the locant
series 1,7,9,10,13,16,18,21,4,22,23,27 is higher than
1,7,9,10,13,16,17,21,4,22,24,27.
A
Module s e n i o r i t y g r a p h :
I
T e t r a c y c l o [ ( O G ) l : 7 ( 3 ) 9 : 1 0 ( 0 6 ) 1 3 : 16(05)17 : 21(1)4 : 22(05)24 : 2 7 ( l ) ] h e p t a c o s a n o d a n e
6
4.
Module
Seniority
Number
Contraction
Node
Seniority
Number
of Nodes
Module
Locants
Assembly
Locants
1
A
C
A
6
2
1-6
2
6
5
1
1-6
-1-5
1-6
7-8
9-14
15--19
1
20
5
1-5
21-25
3
4
5
6
896
B
D
B
-1-2
T e t r a c y c l o [ ( O G ) l : 7(06)9 : 13(06)16 : 19(06)1
tetrac osanodane
Note: The descriptor [(06)1:7(06)10: 13(06)15: 19(06)] is
not correct because the locant series 1,7,10,13,15,19 is higher
than 1,7,9,13,16,19.
Angew. Chem. Inl. Ed. Engl. 18,887-899 (1979)
The concept of the module seniority graph (see Rules N5.2 and N-5.3)enables even very complex assemblies to be
numbered and named with ease. We now illustrate a procedure that has worked well for us in numbering and naming
assemblies. We have deliberately chosen a very complex assembly because it illustrates well the use of the module seniority graph, even though most assemblies normally encountered in chemical substances are much simpler.
.. ...
t
+
A
Fig. 1. Separation of an assembly into its modules.
Module
Descriptor
Module
Seniority
Module
Seniority Number
Assembly
Locants
[Ot 2.1 '.'09,"]
A
1
1-13
(7.14141
C
2
14-22
B
11
45-53
7
D
3
23-29
6
E
8
3641
Number
Module
Structure
of Nodes
ca
L-i
I
*
-
6. A Procedure for Deriving the Correct Numbering
and Name of an Assembly
2
121
F
4
3&31
2
121
F
7
34-35
2
1-21
F
9
4243
1
t
.
54-55
I
0
32
0
33
I
44
56
13
Module
seniority
graph:
I1
,,F G-B-F
I
I
G-D,-C-A-F-E
5
1
Gb
2
1
12
Fs
I
28
' *I
Gio
Octacyclo((012.1"509"3)2 : 2 1 ( 7 . 1 4 1 * ) 2 2 : 24(06.1"4)23 : 30( 2 ) 2 9 : 3 2 ( 1 ) 2 9 : 33(1)8 : 34(2)35 : 36(06)37 : 4 2 ( 2 ) 4 1 : 44(1)11 : 50(09.0'85)46 : 5 4 ( 2 ) 5 2 : 56(l)lhexapentacontanodane
Fig. 2. Illustrative procedure for derivation of mrrect numbering and name of an assembly.
Angew. Chem. Int. Ed. Engl. 18. 887-899 (1979)
897
An assembly, such as the one shown on p. 897, is numbered and named in the following stepwise manner: (1) the
assembly is separated into its modules as indicated in Figure
1; (2) the modules are sorted in order of decreasing number
of nodes; (3) each module is numbered according to Rule N1, N-2, or N-3; (4) the descriptor is derived for each module;
(5) seniority is assigned to each module according to Rule N4.3; (6) the seniority graph is drawn and the module seniority
numbers assigned according to Rules N-5.2 and N-5.3; (7) assembly locants are assigned by renumbering each module according to Rules N-5.1 and N-5.3, or N-5.4; (8) the assembly
locants are added to the structure of the assembly; (9) the assembly name is generated (see Rule N-4.4); and (10) the
name is checked against the structure. This procedure is illustrated in Figure 2.
Nodal names are easily checked against the structure for
accuracy. In the absence of the structure, nodal names provide a wealth of information about the structure. As in von
Baeyer nomenclature, the descriptor portion of a nodal name
contains all the information necessary to derive the structure;
all the rest of the name, while essentially superfluous, provides a check on the descriptor and is also of value for listing
in an alphabetical index.
Preliminary inspection of a nodal name provides much
useful information that aids checking the name and in visualizing the structure. For example, inspection of the name
[7.1414]nonanodane indicates: (1) the structure is acyclic
since there is no “cyclo” term at the beginning of the name
and no zero immediately precedes the first numeral of the
descriptor; (2) the main chain consists of seven nodes and
there are two one-atom branches attached to the fourth node;
and (3) the total number of nodes is nine, obtained by summing the nonsuperscript numerals, which is confirmed by the
term “nona” following the descriptor.
Similarly, inspection of the name bicyclo[O6.1‘.)heptanodane indicates: (1) the structure is cyclic because of the term
“cyclo” before the descriptor and the zero immediately preceding the first numeral of the descriptor; (2) the structure
consists of two rings, since there are two terms in the descriptor and the term “bi” precedes cyclo; and (3) the total number of nodes in the structure is seven, obtained by summing
the nonsuperscript numerals of the descriptor, which is confirmed by the term “hepta” following the descriptor.
Such inspection is especially useful when checking the
name of a complex assembly such as the one generated
above (Fig. 2). From the assembly descriptor, we can see that
there are eight rings in all, obtained by adding the number of
nonsuperscript numerals in the module descriptors that begin with a zero (i. e., 3 + 2+ 1+ 2); thus the numerical prefix
“octa” to the term cyclo should be found in front of the assembly descriptor. By adding the values of all the nonsuperscript numbers, the total number of nodes in the structure is
found to be 56 ( i e . , 1 2 + 1 + 7 + 1 + 1 + 6 + 1 + 2 + 1 + 1 + 2 +
6 + 2 + 1+9 + 2 + 1); this should correspond to the numerical
prefix “hexapentaconta” which is found following the descriptor.
7. Deriving the Structure of an Assembly from its
Name
Inspection of the assembly descriptor is also extremely valuable when deriving the structure of a complex assembly
898
from its name. By using the following name,
Octacyclo[(012.11,50’.’3)2:21(7.1 414)22:24(06.1 ‘.4)23: 30(2)29 : 32(1)
29:33(1)8:34(2)35: 36(06)37:42(2)41:44(1)11: 50(09.01.5)46:54(2)52:
56( l)/hexapentacontanodane,
derived for the complex assembly given in Section 6, we can
learn the following information by inspection of the descriptor: (1) the structure is an assembly of thirteen modules since
Module Descriptor
Structure
Assembly Locants
G3
28@
1
2
H
10
12
I
a
a
33
a
I
11
H
0
2
t
.
1s
34
-
a
43
44
a
56
Fig. 3. Illustrative procedure for derivation of the structure of an assembly from
its name.
there are thirteen descriptors, each enclosed in parentheses,
in the total assembly descriptor defined by the square brackets; (2) four of the modules are cyclic since four module descriptors have a “zero” preceding the first numeral in the
descriptor; (3) the assembly has a total of eight rings since the
four modules defining cyclic structures have a total of eight
terms and the prefix “octa” precedes cyclo in the name; (4)
the assembly has nine acyclic modules, one of which is
branched; and (5) the total assembly has 56 nodes, deterAngew. Chem. Int. Ed. Engl. 18, 887-899 (1979)
mined by summing all nonsuperscript numbers within the
parentheses and confirmed by the numerical prefix “hexapentaconta” following the assembly descriptor.
The structure of this assembly may be derived from the
name as follows: (1) each of the thirteen modules is drawn
and numbered, according to its descriptor, in order of appearance in the name; (2) the assembly numbering is assigned to each module by adding to each locant the total
number of preceding locants; (3) the modules are assembled
in accordance with the locant sets for each pair of modules in
the assembly descriptor; (4) the structure (see Fig. 2) is
checked against the name as outlined above.
This procedure is summarized in Figure 3.
8. Conclusion
We have presented a comprehensive system for numbering
and naming graphs of chemical compounds. The system can
easily be adapted to naming chemical compounds and it
avoids a number of shortcomings apparent in existing nomenclature systems. Not only does this system result in uniformity and a new approach for organic nomenclature, but it
also provides new approaches for the nomenclature of complex coordination, inorganic, and biochemical systems. Future publications will delineate the application of this general system to specific types of compounds.
Received: November 28, 1978 [A 296 IE]
German version: Angew. Chem. 91, 951 (1979)
111 IUPAC: Nomenclature of Organic Chemistry (1969), Sections A and B, 3rd
Edit., and Section C, 2nd Edit. (combined), Buttenvorths, London (1971).
[Z] IUPAC: Nomenclature of Organic Chemistry, Section D (Tentative),
IUPAC Information Bulletin Appendices on Tentative Nomenclature,
Symbols, Units, and Standards, No. 31, August, 1973.
131 IUPAC: Nomenclature of Organic Chemistry, Section E, Stereochemistry
(Recommendations, 1974). Pure App. Chem. 45, 11 (1976).
[4] IUPAC: Nomenclature of Organic Chemistry, Section F, Natural Products
and Related Compounds, IUPAC Information Bulletin Appendices on Provisional Nomenclature, Symbols, Terminology, and Conventions, No. 53,
December, 1976.
[5] IUPAC: Nomenclature of Organic Chemistry, Section G, in preparation.
161 The term “node” has been used for multivalent centers by M. Gordon and
W. B. Temple in A . T. Balaban: Chemical Applications of Graph Theory,
Academic Press, London, 1976, p. 312. This term was introduced by J. J.
Sylvesrer, Am. J. Math. I, 64 (1878) as follows: “The conception of hydrocarbon graphs as ‘trees with nodes, branches and terminals’ ., . [is] exclusively my own and [was] used by me in my communications with Professor
Crum Brown on the subject and stated by me in a letter to Professor Cayley
who has adopted [it] as the basis of his own isomerical researches”. It should
be noted that it is convenient in nodal nomenclature for the term “node” to
include terminals, (i. e., “univalent” centers) and for the term “ g r a p h to be
conceptually distinct from chemical structures with specified nodes and
bonds.
[7] K. Hirayama, Tetrahedron Lett. 1972, 2109-21 12; Th. Kaufmann, Tetrahedron 2X, 5183 (1972).
[8] As in the extended von Baeyer nomenclature system, the descriptor is sufficient, by itself, for the derivation of the structure in the nodal system.
(91 In contrast to classical organic nomenclature, all acyclic nodes not interrupted by cyclic nodes are treated together as one unit.
[to] The sum of the numbers denoting the lengths of the chains is equal to the
total number of nodes and, since the locants for the attachment of chains are
indicated by the superscript numbers, the descriptor itself is sufficient for
deriving the structure. The same is true in the extended von Baeyer system
currently In use.
Angew. Chem. Int. Ed. Engl. 18, 887-899 (1979)
[I 11 Since the lengths of the branches are cited in the order of their numbering,
i. e., in order of decreasing length, the only difference occurs in the superscript locants (cf. Rule N3.4).
[I21 The multiplying prefixes are the same as given by Rule A-2.5 in [ l ] and Table 111, p. 142, in [2], except that the prefix “mono” is not used and-in accordance with the most recent recommendation of CNOC (see [24])-the
prefix for twenty is spelled “icosa” rather than “eicosa”.
[13] As indicated in Section 3, for convenience only, we are illustrating the principles of nodal nomenclature mainly with graphs derived from organic
structures, and we are using the general ending “-ane” of classical hydrocarbon nomenclature. However, this is not meant to imply that nodal nomenclature is designed only for use in substitutive nomenclature. Because the
ending “-nodane” could convey the concept of a fully hydrogenated parent
system in substitutive nomenclature. the selection of another ending derived
from the same root “nod” is under consideration for use in the most general
applications of nodal nomenclature.
1141 To facilitate the comparison between nodal nomenclatiire and traditional
organic nomenclature, most of these examples correspond to the acyclic hydrocarbons given in Section A in [I].
[IS] In nodal names for monocyclic graphs, the prefm “cyclo” and the “zero” are
mutually redundant, as are the Arabic numbers and the multiplying prefix.
They are retained, however, in order to distinguish monocyclic modules
from unbranched acyclic modules in assembly descriptors. Without the zero
denoting the presence of a ring, a name such as “cyclo[(5)1:6(4)]nonanodane” is ambiguous: it could represent either “cyclo[(O5)1: h(4)lnonanodane” or “cyclo[(5)1: 6(04)]nonanodane”.
1161 Thus, two rings joined only by a single common (spiro) atom do not, together, constitute a main ring, but form a main ring and a bridge.
[17] Occasionally, as shown in the examples below, a longer bridge is present,
but cannot he numbered until after a shorter bridge has been numbered.
Tricycle[ 06. 31”48’8]tridecanodane
Tetracyclo[0 10. 1”4211’”05”0
1tridecanodane
[18] The total number of terms in the descriptor of a polycyclic graph is the same
as the number of rings and the sum of the nonsuperscript numerals is equal
to the number of nodes in the total graph.
[19] Seniority order for polycyclic modules (Rule N4.3) does not follow the
method of selection for polycyclic descriptors (Rule N-3.6). Selection of the
descriptor for polycyclic graphs follows the method used for numbering the
structure. At each step, the numbering continues by the longest possible
bridge attached to nodes with the lowest locants in the part of the graph previously numbered. As a consequence, all numerals representing either
bridge lengths or locants are successively compared in their order of appearance in the descriptor, preference being given to the descriptor where, at the
first difference, either the longest bridge or the lowest locant occurs. On the
other hand, for selecting the senior module of an assembly. it seems to be
more consistent with usual practice to compare first the bridge lengths and
then, only if a choice remains, superscript locants. It should be noted that, in
many cases, either method of selection will lead to the same result. Comments on this decision will be welcome.
(20) The number of rings in a polycyclic system is equal to the minimum number
of scissions needed to convert the system into an acyclic structure (see Rule
A-32.12 in [I]).
[21] For some of these examples, the trivial or semisystematic name of the
corresponding hydrocarbon is given and marked by an asterisk.
1221 Symmetry of the module seniority graph often precludes the determination
of the correct order for numbering of the modules attached to the principal
module, or the choice of the principal module from two or more modules of
the same highest seniority.
[231 Selection rules for numbering the module seniority graph (Rule N-5.3)differ from those applied to acyclic graphs (Rule N-I) because module seniority graphs deal with constituent units (modules) which may greatly differ in
structural complexity. Accordingly, rules for the module seniority graph
take into consideration the nature of the contraction nodes, while, according
to Rule N-I, the nature of the nodes does not affect the numbering of the
graph.
[24] Nofe added in proof: I141 have been revised and published as IUPAC:
Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H. Pergamom Press, Oxford 1979.
899
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