Phenanthrene nomenclature

Consider the two phenanthrene annulated NHC in Figure 1.26, they differ only in the position of the methyl group in the tolyl N-substituent. They have the same % value, but the o-tolyl substituted one is a monomeric NHC whereas the p-tolyl isomer is a dimeric tetraaminoethylene at ambient temperature [124], The A j, nomenclature is able to distinguish between the two and explain the monomeric or dimeric structure. The greater A value introduced by the < -methyl group is stericaUy active, whereas the greater A value introduced by the p-methyl group is sterically inactive. 

The lUPAC name of hexahelicene is phenanthro[3,4 d]phenanthrene In a simplified nomenclature for the helicenes introduced by M. S. Newman, the number of the annellated aromatic rings is set in brackets before the helicene name hexahelicene = t6]helicene. Today, according to the building blocks composing the helicene, one differentiates carbohelicenes, heterohelicenes, double helicenes, bihelicenyls, metallohelicenes and cyclophanohelicenes. The names dehydrohelicene and circulene are used for some related compounds (v.i.). 

The parent compound (1) was discovered in 1891 by Tauber, who called it diphenyleneazone, and later phenazone. Unfortunately, the latter name was at one time also used for 2,3-dimethyl-l-phenylpyrazol-5-one (anti-pyrine). More recently 1 has been called 3,4-benzocinnoline and now benzo-[c]cinnoline, using Chemical Abstracts nomenclature. The numbering shown is that currently used Beilstein s Handbuch employed numbering analogous to that used for phenanthrene. 

At this point, we can introduce an entirely different system of nomenclature that is nevertheless accepted by lUPAC and is extremely valuable in multicyclic and bridged saturated systems. This is the replacement system, where the hydrocarbon name that would correspond to the entire ring structure, as if no heteroatom were present, is stated, and then given a Hantzsch-Widman prefix and number for the heteroatom(s). Thus, phenanthridine shown previously has the ring framework of the hydrocarbon phenanthrene, with N at position 5. The replacement name would be 5-azaphenanthrene. 

Structure nomenclature All S. are based on the tetracyclic carbon skeleton of gonane (=perhydrocyclo-penta[a]phenanthrene) which possesses 6 centers of chirality (asymmetric centers). Thus there are 2 =64 theoretically possible stereoisomers but only few of them are realized among the S. 

The nomenclature of amines is exceptional. By very long custom radical names may be attached to the ending amine, as in ethylamine but it is equally correct to add amine to the parent name, as indicated in Table 4, giving names such as phenanthren-1-amine, quinolin-8-amine, or even ethanamine. The latter practice is often reserved for more complex cases but that is not a necessary limitation. The same alternatives exist for ammonium salts. Secondary and tertiary amines are treated as substitution products of the most complex constituent primary amine, with N- prefixes when substitution elsewhere might be reasonable, as in triethylamine, dimethylamine,... 

In addition, names may be formed from any hydrocarbon by indicating replacement of a ring member by, for instance, oxygen, sulphur, or nitrogen by oxa-, thia-, aza-prefixes, respectively. The numbering of the hydrocarbon is retained by this procedure, and if more than one kind of heteroatom is present they are cited in a prescribed order (e.g.j that just given). An example would be 8ff-7-thia-l,9-diaza-phenanthrene (XXI). This nomenclature must be applied to the hydrocarbon parent , not to a... 

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