Acene linear fused rings

Some fused systems are named systematically by using a multiplicative prefix in front of an ending representing a well-defined arrangement of cycles. For instance, the ending -acene, taken from anthracene, indicates a linear arrangement of benzene rings, as in tetracene, pentacene, etc. 

We earlier recalled that one can build a huge number of molecules by simply assembling CeH rings, a scheme that was summarized in Table 1.4, and that a solid such as graphite can be obtained in this gedanken synthesis. Let us briefly discuss the case of linear acenes, which are linear polycyclic aromatic hydrocarbons (PAHs) composed of laterally fused CeHe rings. 

The names of hydrocarbons containing five or more fused benzene rings in a straight linear arrangement are formed from a numerical prefix as specified in Rule A-1.1 followed by -acene . [Examples on p. 255]. 

Fused Polycyclic Hydrocarbons. The names of polycyclic hydrocarbons containing the maximum number of conjugated double bonds end in -ene. Here the ending does not denote one double bond. Names of hydrocarbons containing five or more fixed benzene rings in a linear arrangement are formed from a numerical prefix (see Table 11.4) followed by -acene. A partial list of the names of polycyclic hydrocarbons is given in Table 1.2. Many names are trivial. 

Acene A linear arrangement of fused benzenes, such as the three-ring system anthracene. 

Two other common subcategories of PAH are the acenes and the phenes. The acenes consist of benzoid rings fused in a linear arrangement, e.g., naphthalene, anthracene, naphthacene, etc. The phenes consist of benzenoid rings fused in an angular arrangement, e.g., phenanthrene, benzo[a]anthracene, etc. 

Cata-condensed polycyclic hydrocarbons contain benzenoid rings such that each fused carbon atom is common to no more than two rings. The benzenoid rings may be linearly annelated (acenes), as in the series naphthalene (19), anthracene (20), and naph-thacene (21), or they may be angularly annelated, as in phenanthrene (22), benz[a]anthracene (23), benzo[c]phenanthrene (24), chrysene (25), and tri-phenylene (26). Except for some isolated examples... 

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