Structure based naming

In this chapter are set out the most important of the trivial names in current use, and the several systems that generate structure-based names. The emphasis is on parent... 

Many classes of natural product possess heterocyclic components (e.g. alkaloids, carbohydrates). However, their structures are often complex, and although structure-based names derived by using the principles outlined in the foregoing sections can be devised, such names tend to be impossibly cumbersome. Furthermore, the properties of complex natural product structures are often closely bound up with their stereochemistry, and for a molecule containing a number of asymmetric elements the specification of a particular stereoisomer by using the fundamental descriptors (R/S, EjZ) is a job few chemists relish. 

Note Structure-based names of tactic polymers are formed before the application of adjectives designating tacticity thus, syndiotactic poly(methylmethylene) is preferred to syndiotactic poly(l,2-dimethylethane-l,2-diyl) because a shorter repeating unit is identified, in conformity with the rules in Ref. 3. 

The possible line repetition groups are listed below, with examples. (The structure-based name is given first, the source-based name second, in each case.)... 

Polymer (source-based name, structure-based name)... 

The formation of a systematic name for a polymer requires the identification and naming of a preferred constitutional repeating unit (CRU). This basic name is then modified by prefixes, which convey precisely the structural identity of the polymer in question. Such names are referred to as structure-based names. However, polymers can also be named as being derived from a monomer (or precursors), named according to lUPAC rules. Such names are referred to as source-based names. Over the years, rules for determining polymer nomenclature under these two systems have developed in parallel. An example of the modification of the lUPAC name of an organic molecule to lUPAC structure-based and source-based names of a polymer is illustrated below. 

Structure-based name poly(l-propylethane-l,2-diyl). Source-based name poly(pent-l-ene)... 

Although source-based names are usually simpler than structure-based names, historically the Commission has not systematically recommended source-based names for... 

A homopolymer that can be represented by a source-based name can usually be given a completely unambiguous structure-based representation, and such a representation should therefore be ideally accompanied by a structure-based name. A source-based name was therefore deemed redundant in these cases. 

Despite the Commission s long-standing position, the scientific community has continued to use source-based nomenclature for homopolymers such as polystyrene and poly(vinyl acetate) because of their simplicity, convenience and obvious relationship with the monomers from which the homopolymers are prepared. The Commission therefore decided to recommend source-based nomenclature as an alternative official nomenclature for homopolymers in a 2001 publication [2]. Consequently, both source-based and structure-based names are now available for most polymers. The names of monomers in the source-based names may be traditional or semi-systematic, if well established by usage, and not necessarily only those retained in the 1993 A Guide to lUPAC Nomenclature of Organic Compounds [3]. 

Structure Structure-based name Source-based name Traditional name... 

The nomenclature of regular polymers can denote stereochemical features if the CRU used is the configurational base unit [10], i.e. a CRU having one or more sites of defined stereoisomerism in the main chain of a polymer molecule [11]. Structure-based names are then derived in the usual fashion. The various stereochemical features that are possible in a polymer must first be defined. 

Beeause both the souree-based and structure-based names of polymers can sometimes be lengthy, abbreviations are frequently used for common industrial polymers. The lUPAC reeognizes that there ean be advantages in some cases to the use of abbreviations, but urges that each abbreviation be fully defined the first time it appears in a text and that no abbreviations be used in titles of publieations. Because of the inherent difficulties in assigning systematie and unique abbreviations to polymeric structures, only a short list has the lUPAC s offieial sanetion [12]. 

The fundamental principles and the basic rules of the structure-based nomenclature are given first, accompanied by detailed extensions and applications. An Appendix contains names of common subunits as well as a list of acceptable source-based names, along with the corresponding structure-based names, of common polymers. There is no strong preference for the use of structure-based names over source-based names for polymers where the latter are clear and unambiguous, but for certain purposes one system of naming may be preferred to the other. 

The Commission recognized that a number of common polymers have semisystematic or trivial source-based names that are well established by usage it is not intended that they be immediately supplanted by the structure-based names. Nevertheless, it is hoped that for scientific communication the use of semisystematic or trivial source-based names for polymers will be kept to a minimum. 

For the following idealized structural representations, the semisystematic or trivial source-based names given are approved for use in scientific work the corresponding structure-based names are given as alternative names. Equivalent names for close analogues of these polymers [e.g. other alkyl ester analogues of poly(methyl acrylate)] are also acceptable. 

It may also be useful at times to provide both source- and structure-based names for the same polymer. For a couple of examples below (6 and 11), references within this document are given to the corresponding constitutional repeating units and their names. 

Irregular polymers or bloeks are named by placing the prefix poly before the structure-based names of the eonstitutional units, collectively enclosed in parentheses or brackets, with the individual eonstitutional units separated by oblique strokes. A typical name derived from this new system is... 

The proeedure for structure-based naming of irregular single-strand polymers is as follows ... 

Structure-based names [2-4, 5, 9] are given first, followed by source-based names or traditional names [2-4, 9], if these exist. 

Structure-based names are given first [5] followed, if necessary, by an explanation (in parentheses) and a formula segment of the macromolecule. Then the monomeric or constitutional units necessary to describe the complete structure are given followed by the proposed formula. 

Source-based copolymer names [6] are given first, followed by an explanation in parentheses before the proposed formula. Structure-based names [5] are given for star copolymers in the notes to examples 4.4-E6 and 4.4-E7... 

Note The buta-1,3-diene is exelusively ineorporated by 1,4-oligomerization whieh eannot be reflected in the souree-based name. The structure-based name is bis[poly(but-2-ene-1,4-diyl)] [poly(l -phenylethane-1,2-diyl)] [poly(2-phenylethane-1,2-diyl)]silane. 

Most trivial names, such as polystyrene, are source-based names. Hitherto, the Commission has not systematically recommended source-based names for homopolymers because it considered that the more rigorous structure-based names were more appropriate for scientific communications. However, since the publication of Nomenclature of Regular Single-Strand Organic Polymers in 1976, scientists, in both industry and academia, have continued to use trivial names. Even the Commission itself adopted (1985) a source-based nomenclature for copolymers because of its simplicity and practicality. Based on these facts, the Commission has now decided to recommend source-based... 

Source-based name polystyrene Structure-based name poly( 1 -phenylethane-1,2-diyl)... 

Note 5 In a structure-based name, a dash denotes a iunction between blocks (see example 2.1 in [3]). 

Structure-based name poly(l,2,4-oxadiazole-3,5-diyl-l,4-phenylene)... 

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