11 Functional Compounds of Symmetrical Structure
Many
polyfunctional compounds, particularly those in which both cyclic and acyclic components are present, possess sufficient sym metry in their structures to warrant treatment by a specialized extension of substitutive nomenclature. This chapter describes the naming of compounds in which the structural unit (chain or ring) carrying the principal function occurs more than once in the molecule, each such replicated unit being linked to its counterparts through a single central structure comprising one or more chains and/or rings. The special "inside out" treatment recommended below for such functionally symmetrical compounds makes possible both retention o f the suffix name for the principal function and application of the general principle of organic nomenclature whereby, whenever possible, like groups are treated alike.
Naming o f nonfunctional symmetrical structures— i.e.,cyclic-acyclic hydrocarbons and cyclic-acyclic heterocyclic systems whose functional character arises only from hetero atoms which are part of a ring — is described in Chapters 3 and 6, respectively. Recommended Nomenclature Practice If the symmetrically replicated chain or ring system carries only those kinds of functional groups that are always named as prefixes (first part of Table 8.1), the most centrally located chain or ring system is chosen as the parent compound, and no specialized treatment is required.
If the symmetrically replicated chain or ring system carries one or more kinds of functional group for which suffix names are provided (second part of Table 8.1), one of these is selected as the principal 84
11.
85
Symmetrical Structure
function and used in deriving the name of the parent compound. Naming of the parent compound is completed by attaching the usual prefix names for substituents, except that the substituting central portion of the molecule connecting the several replicates of the parent compound is named by use of special prefix names denoting more than one point of attachment per substituting group. The position in each parent compound unit at which it is attached to the central connecting structure is indicated by a number locant, using prime markings to distinguish among the several parent compound units present.
COOH
HOOC
HOOC
^-O
^-COQH
^CK^COOH N-—CH2COOH CH COOH
4,4'-Methylenedibenzoic acid
4,4'-Oxydibenzoic acid
Nitrilotriacetic acid
2
HOCH CH 2
H NCH CH 2
CH CH OH 2
2
2
2
2
CH CH NH 2
2
2,2'-( 1,4-Phenylene)diethanol
2
2,2',2",2"'-(l,4,5,8-Naphthalenetetrayl) tetrakis (ethylamine) H NCH CH 2
2
2
CH CH NH 2
2
2
When the central connecting structure comprises several groups (chains or rings) that must be named individually, each o f these is named as a multivalent substituting group (see Table 11.1). Citation begins with the group at the center and proceeds outward to the points of attachment to the several replicated parent compound units.
4,4'- [Iminobis( 1,4-pbeny leneoxyethylene) ] di-l-naphthol
86
NOMENCLATURE OF ORGANIC COMPOUNDS
The respective points of attachment o f replicated parent compound units need not be the same for each unit.
COOH
COOH 2,3'-[(3-Chlorotetramethylene)dioxy] bis(4-pyridinecarboxylic acid) Discussion The "inside out" method recommended above for naming polyfunctional compounds of symmetrical structure should be used only in cases where the outermost replicated structural unit contains a functional group that can be designated the principal group and named by use of a suffix. However, Chemical Abstracts has taken advantage of the technique in forming index names for symmetrical heterocyclic compounds even when no such principal functional group is present— e.g., 2,2'-methylenedipyridine (for di-2-pyridylmethane). Except for indexing purposes such as this, where it is considered important to use the name of the heterocyclic system as the main subject entry, extension of the "inside out" method of naming to nonfunctional compounds is neither desirable nor warranted. A further requirement for proper use o f the "inside out" method is that i n the central connecting structure o f the symmetrical compound being named, each "spoke of the wheel" must be identical. However, the centermost chain or ring system— ie., the "hub"—need not be symmetrical within itself. These principles are illustrated in the examples shown above.
Table 11.1. Typical Multivalent Groups Used in Naming Compounds of Symmetrical Structure Prefix Name Azo
Group —N=N—
1,2,4-Benzenetriyl
C H CH6
Benzylidene
5
I
C H < -CH CH=CHCH -COCH CH CO6
5
2
2
-C=0
2
2
Benzylidyne 2-Butenylene Butanedioyl Carbonyl
Symmetrical Structure Table 11.1 Continued Group
Prefix Name
—NHCONH— -OC(0)0-
Carbonyldiimino Carbonyldioxy 1,4-Cyclohexylene
o
Cyclohexylidene 1,2-Diazanediyl Dioxy Dithio Ethanedioyl Ethenylene Ethylene
—NHNH— -00-
-ss-coco-CH=CH—CH2CH2—
-OCH CH 02
2
Ethylenedioxy
\
CH3CH—
Ethylidene
I
CH CI -C5C—NH— 3
Ethylidyne Ethynylene Imino Isopropylidene Methylene Methylenedioxy
I
(CH ) C-CH -0CH 03
2
2
2
I H
