Nomenclature of Ring Systems

The nomenclature of ring systems containing the partially or fully hydrogenated monocyclic, bicyclic, and tricyclic fused 1,2-oxazine ring skeleton are shown in Figure 1. 

Stelzner Method. This is a general method of applying replacement nomenclature to ring systems it differs from the Chemical Abstracts procedure in that replacement principles are applied in all cases to the name of the hydrocarbon with the same bond distribution in the rings as the heterocycle to be named. This leads to no difference for monocycles (see examples 1-3), but in the case of fused skeletons the parent hydrocarbon of a fully unsaturated heterocycle is frequently a partially hydrogenated molecule. The parent hydrocarbon name for application of either replacement method can be trivial or a name derived by fusion principles (as above). The examples 21-24 of both... 

The numbering of the skeleton in a ring system is generally a consequence of the way in which the skeleton is named. In order to avoid confusion as to the peripheral numbering sequence and locations of substituents in the fused systems, structural formulae are drawn as in Chemical Abstracts in accordance with the rules of heterocyclic nomenclature. Thereby the reader is not required to possess detailed knowledge of the elaborate series of priorities used in the structural presentation and numbering of ring systems. 

Figure i.i. Nomenclature of porphyrin system, Chlorin is the basic skeleton of natural chlorophylls. Notice the 7,8-dihydro group and pentacyclic ring V, Chlorin does not contain ring V, Porphin is the basic skeleton of porphyrins (alkyl porphins), Etioporphins contain methyl and ethyl groups in the Q-positions, etioporphyrin I is M, E, M, E,... 

Seniority of ring systems is decided by applying 12 criteria which are, in general, in agreement with the lUPAC recommendation C.0.14 (p. 101 in ). The senior chain, i.e., the chain upon which the nomenclature and enumeration of all atoms in the structure will be based, is chosen by applying successively 10 criteria formulated by the lUPAC recommendation C.0.13 (p. 97 in ). 

The names cited are common names which have been m widespread use for a long time and are acceptable m lUPAC nomenclature We will introduce the systematic nomen clature of these ring systems as needed m later chapters... 

When the aldehyde group is directly attached to a carbon atom of a ring system, the suffix -carbaldehyde is added to the name of the ring system, e.g., 2-naphthalenecarbaldehyde. When the aldehyde group is separated from the ring by a chain of carbon atoms, the compound is named (1) as a derivative of the acyclic system or (2) by conjunctive nomenclature, for example, (1) (2-naphthyl)propionaldehyde or (2) 2-naphthalenepropionaldehyde. 

Organic ring systems are named by replacement nomenclature. Three- to ten-membered mono-cyclic ring systems containing uncharged boron atoms may be named by the specialist nomenclature for heterocyclic systems. Organic derivatives are named as outlined for substitutive nomenclature. The complexity of boron nomenclature precludes additional details the text by Rigaudy and Klesney should be consulted. 

Heteroeyeles structurally based on the phenalene ring system form an interesting elass, frequently possessing distinetive eolours. With nitrogen as the central atom we have the unstable 9b-azaphenalene (24), whieh has only fairly reeently been prepared and is still comparatively little studied (76JCS(Pl)34l). The cyclazine nomenclature is commonly applied to this and related compounds thus, (24) is (3.3.3)cyclazine. With further aza substitution, in positions alternant to the central atom, their stability increases the heptaazaphenalene (25) is (thermally) a very inert compound, derivatives of which, e.g. the triamine, have been known since the early days of organic chemistry (see Chapter 2.20). 

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