PAHs peri-condensed

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. 

Pyrolytic PAH distributions in ancient sediments sometimes differ from those typical of Recent sediments in exhibiting enhanced levels of the more highly peri-condensed structures, especially benzofe]pyrene, benzo[gfe]perylene and coronene (Fig. 7.4 Killops Massoud 1992). The reasons are as yet unknown but may reflect the effects of either different formation conditions or varying geochemical processes over geological time periods. 

We previously mentioned that excitation localization indices L point to photoactive sites in excited molecule, and as such they can serve as suitable photochemical indices. For instance, anthracene and tetracene undergo photoaddition and photooxidation primarily at the peripheral atoms of central rings, and the diagrams in Table 14.1 agree with this fact. In peri-condensed PAHs, such as pyrene and... 

Another major class of PAHs consists of peri-condensed polyarenes, for example, pyrene, ovalene, hexa-peri-hexabenzocoronene (HBC), etc. (Fig. 3.3). 

The quarterrylene (49) and other o/igo(peri-naphthylene)s, which are large condensed PAHs with interesting fluorescence behavior, have been synthesized in an overall three-step aryl-aryl coupling sequence from suitably substituted naphthalenes. Electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) investigations indicate, that this reaction proceeds via the dianions of 47 and 48, which were oxidized with cadmium chloride to the neutral hydrocarbons. 

---