Functional groups nomenclatural priority

Alternative names are shown in some cases this should emphasize that there is often no unique correct name. Sometimes, it can be advantageous to bend the rules a little so as to provide a neat name rather than a fully systematic one. Typically, this might mean adopting a lower priority functional group as the suffix name. It is important to view nomenclature as a means of conveying an acceptable unambiguous stmc-ture rather than a rather meaningless scholastic exercise. Other examples will occur in subsequent chapters, and specialized aspects, e.g. heterocyclic nomenclature, will be treated in more detail at the appropriate time (see Chapter 11). Stereochemical descriptors are omitted here, but will be discussed under stereochemistry (see Sections 3.4.2 and 3.4.3). 

Functional groups in the -position may lead to priority in notation. For example, 75 is called jff-aminocro tonic acid nitrile and 76 is ethyl jff-aminocrotonate. Further examples pertaining to the nomenclature of complex enamines may be found in the next section in Schemes 2 to 5. 

Many organic compounds contain more than one functional group. When one of those functional groups is halo (X-) or alkoxy (RO-), these groups are named as substituents as described in Sections 7.2 and 9.3B. To name other polyfunctional compounds, we must learn which functional group is assigned a higher priority in the rules of nomenclature. Two steps are usually needed ... 

Number the carbon chain to give the lower number to the highest priority functional group, and then follow all other rules of nomenclature. Examples are shown in Figure B.1. 

The designation of central atom and ligands, generally straightforward in mononuclear complexes, is more difficult in polynuclear compounds where there are several central atoms in the compound to be named, e.g. in polynuclear coordination compounds, and chain and ring compounds. In each case, a priority order or hierarchy has to be established. A hierarchy of functional groups is an established feature of substitutive nomenclature Table VI shows an element sequence used in compositional and additive nomenclature. 

Aromatic" compounds are those derived from benzene and similar ring systems. As with aliphatic nomenclature described above, the process is determining the root name of the parent ring determining priority, name, and position number of substituents and assembling the name in alphabetical order. Functional group priorities are the same in aliphatic and aromatic nomenclature. See p. 676 for the list of priorities. 

The term "heteroatom" applies to any atom other than carbon or hydrogen. It is common for heteroatoms to appear in locations that are inconvenient to name following basic rules, so a simple system called "replacement nomenclature" has been devised. The fundamental principle is to name a compound as if it contained only carbons in the skeleton, plus any functional groups or substituents, and then indicate which carbons are "replaced" by heteroatoms. The prefixes used to indicate these substitions are listed here in decreasing priority and listed in this order in the name ... 

Moreover, NMR was revolutionary in provoking a Gestalt switch (to borrow Kuhn s phraseology) in the chemists perceptions. Earlier, molecules were identified by their functional groups, carbonyls, hydroxyls, and the like, which were like beacons (as reflected in chemical nomenclature, in its affixes and priorities). Now, especially at the beginning of... 

Fig. 13.18. Stereochemical nomenclature for arylethanolamines versus aryloxypropanolamines. The relative positions in space of the four functional groups are the same in the two structures however, one Is designated (R) and the other (S). This Is because the introduction of an oxygen atom into the side chain of the aryloxypropanolamine changes the priority of two of the groups used in the nomenclature assignment.

Functional Groups in Order of Priority for the Selection of the Name Suffix in Systematic Steroid Nomenclature... 

The lUPAC nomenclature for carboxylic acids uses the name of the alkane that corresponds to the longest continuous chain of carbon atoms. Tlie final -e in the alkane name is replaced by the suffix -oic acid. The chain is numbered, starting with the carboxyl carbon atom, to give positions of substituents along the chain. In naming, the carboxyl group takes priority over any of the functional groups discussed previously. 

Order of precedence of functional groups A system for ranking functional groups in order of priority for the purposes of IUPAC nomenclature. 

In Section 7.2, we saw that a carbonyl group has a higher nomenclature priority than an alcohol or an amino group. However, all carbonyl compounds do not have the same priority. Nomenclature priorities of the various functional groups, including carbonyl groups, are listed in Table 17.1. 

Chapters 1,2, and 3 of this book have dealt in some detail with the nomenclature rules for parent structures and the wealth of different functional compound classes based there upon. The present chapter will recapitulate once again in a more summary manner the most important directives for the construction of the complete names of more complex compounds. This entails a reconsideration of the question of priorities for ring and chain systems already briefly approached in the pertinent sections of Chapter 1. Since functional groups must ultimately be included in the decisions, extension of the priority rules becomes imperative, as will be shown in the following sections. 

---