Peri-Condensed Aromatic Hydrocarbons

Peri-condensed aromatic compounds compounds based on angular condensed aromatic hydrocarbon systems, e.g., phenanthrene, chrysene, picene, etc. 

The fused 3+ ring aromatics in petroleum include both cata- and peri-condensed stmctures (see Table 4, Fig. 8). The cata-condensed species are those stmctures where only one face is shared between rings, the peri-condensed molecules are those that share more than one face. The fused ring aromatics form the class of compounds known as polynuclear aromatic hydrocarbons (PAH) which includes a number of recognized carcinogens in the 4+ ring family (33). Because of the potential health and environmental impact of PAH, these compounds have been studied extensively in petroleum. 

Although the great majority of petroleum and coal-based pitch materials, as well as model compounds such as polyvinyl chloride, acenaphthylene, decacyclene and polynuclear aromatic hydrocarbons, form anisotropic graphitizable carbons, it is an almost impossible task to predict the type of optical texture of a coke from an elemental analysis of the pitch. The size, shape and reactivity of peri-condensed polynuclear aromatic molecules in the products of pyrolysis of a pitch play a more important role in determining optical texture. 

This mode of cyclization opened a new access74 to the stable, tetracyclic peri-condensed, nonbenzenoid aromatic hydrocarbon dicyclopenta(e,f—k,l)heptalene (.159), also named73 azupyrene. The 4,5-cyclopentenoazulene (156) needed was formed in 28% yield by a Hafner synthesis from the pentamethinium salt (155)75 and sodium cyclopentadienide ... 

Figure 28. The structures of peri-condensed polycyclic aromatic hydrocarbons studied 10, pyrene 11, benzo((f)pyrene 12, perylene 13, benzo(a)pyrene 14, benzo(c,d,e)pyrene 15, anthranthrene 16, coronene.

Dias JR (1984a) Isomer Enumeration of Nonradical Strictly Peri-Condensed Polycyclic Aromatic Hydrocarbons. Can J Chem 62 2914... 

Dias JR (1986) A Periodic Table for Polycyclic Aromatic Hydrocarbons - Part IX -Isomer Enumeration and Properties of Radical Strictly Peri—Condensed Polycyclic Aromatic Hydrocarbons. J Mol Struct (Theochem) 137 9... 

The procedure outlined applies to all nonconvex lattices, the inner dual of which is a nonconvex polygon. In Figure 2.9, we have illustrated the Kekule valence structure counts for peri-condensed benzenoid lattices considered by Clar in his booklet The Aromatic Sextet [29]. This time, we only show the result in the top benzene ring leaving it to the readers to flu in the empty benzene rings and verify, as an exercise, that the count shown is correct In the next section, we will briefly outline the count of Kekule valence structures for a more general class of benzenoid hydrocarbons. 

There has been a recent attempt to combine MP2/ 6-31G //HF/6-31G calculations with simple carbon substructure parameters as an accurate approach to correlating and predicting the enthalpies of formation of cata- and peri-condensed unsubstituted polycyclic aromatic hydrocarbons. The electronic energies provide the nonadditive electronic effects, and the carbon-structure parameters model the additive effects. The quality of the multilinear regression was... 

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