Nodal nomenclature

As a consequence of the complex molecular structures, such nomenclatures are not without complications and require numerous rules. However - unlike the IUPAC [46] or nodal nomenclature [47] - owing to their modular structure they quickly reveal important individual characteristics (number of generations, number of terminal groups), which is of benefit in the laboratory and also in computer searches. 

Rule 12 Arene units are counted as a chain member by analogy with nodal nomenclature [47]. Ring atoms are numbered according to the IUPAC rules. 

Unlike nodal nomenclature, the proposed system has no need to introduce a word stem, such as -nodane. 

As the next examples, attention is directed to the newer, mathematically more sophisticated, nodal nomenclature [93]. In this system all atoms (except hydrogen) are initially regarded as points (nodes) in a graph, which are all... 

Fig. 14 The graphic picture for many trianodanes in nodal nomenclature...

Fig. 15 A molecule having two equally acceptable nodal nomenclature names, rather than a single canonical name.

Note that the examples selected in the two original nodal nomenclature reports ([19] and [20]) and in the Dyson system [49] reports are all from the much simpler class of alkanes. Moreover, both the nodal and the Dyson systems have an increase in complexity when naming molecules having multiple types of atoms, a disadvantage that the proposed nomenclature system does not have. To the contrary, because atomic symbols are included in the first "layer of information" about a chemical moiety, there is no need to create a second layer of information in which the names of the different atoms are listed. This inclusion of atom symbols immediately makes for a more user-friendly nomenclature, especially for rapidly scanning a name to see whether it is the moiety under consideration. 

Because one of the motivations in creating the proposed nomenclature system was predicated on its interface with the computer, there is no need for a word-stem, such as the suffix "-nodane" created in nodal nomenclature. If one wishes to make the system more user-friendly, especially for the student user, such a word-stem could easily be included however, a problem with such an inclusion is that it encourages the inclusion of other functionalities so that eventually several of the difficulties that the system has eliminated will be reintroduced. 

One of the main reasons why nodal nomenclature [42] was created was that the IUPAC organic nomenclature did not allow for assigning unique canonical names to members of the class of molecules referred to as "cyclophanes" a problem that would not have arisen had beta bonds been available. This is not to devalue the many virtues of nodal nomenclature, rather merely to show how the proposed system nomenclates these compounds without difficulty. 

There are no "parts of the structure that are to be excluded from the portion of the structure for which general nodal nomenclature is to be applied",... 

There is no need for any artificial word ending, such as ane, ene, yne, ol, al, etc. in IUPAC organic nomenclature, ide, ate, ite, ic vs. ous acid, etc. in IUPAC inorganic nomenclature, as well as nodane in nodal nomenclature. 

One of the main motivations for the development of nodal nomenclature was to be able to compensate for inadequacies that prevented the assignment of a consistent set of canonical names to selected, then recently formulated, molecules — especially the cyclophanes. 

This name, however, could be somewhat simplified if one agrees to follow the sequential locant assignment scheme of nodal nomenclature [45]. In this way similar bridges may be listed together with the resultant name being ... 

Whereas neither I.U.P.A.C. nor nodal nomenclature bother to extend their system to what is, at present, a very small group of topologically restrained compounds, the proposed system allows for a simple extension to the set of catenanes and rotaxanes. Also, one may readily adapt this system to canonically naming endothelial compounds, such as endothelial fullerenes, etc. Moreover, extension to "chemical" knots having multiple interconnections and windings, without having to resort to the tedium employed by Schill to extend I.U.P.A.C. nomenclature to these compounds, is straightforward. 

The connectivity in the molecular framework is indicated by a nodal descriptor, which is placed in square brackets immediately before the terms catena , cycle or catenacycle . The atoms are numbered according to the general nodal nomenclature regardless of their identity. Only in the case of ambiguity are the identities of the atoms taken into consideration. 

N. Lozac h and A.L. Goodson, "Nodal Nomenclature. IL Spedfic Nomendature for Parent Hydrides, ftee Radicals, Ions and Substituents, Angew. Chem. In press. 

The interesting suggestion of so-called nodal nomenclature came from Lozac h et al. in the 1970s. As its name implies it sets out to describe chemical structures by considering... 

More recently nodal nomenclature was addressed again by Polton. He has proposed a very interesting new method of nodal numbering for cyclic and acyclic structures which can be obtained by a computer algorithm directly from the connectivity matrix. It differs from the methods presented by Lozac h as well as from that applied in the HIRN system. It is still open for investigation if the method will eventually show its superiority. 

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