Benzo perylene structure

PAHs also generally have well-structured emission spectra (see Figs. 10.6-10.10) and relatively large fluorescence quantum yields. For example, in degassed n-heptane at room temperature, the fluorescence quantum yields are as follows fluoranthene, 0.35 benz[ ]anthracene, 0.23 chrysene, 0.18 BaP, 0.60 BeP, 0.11 and benzo[g/zi]perylene, 0.29 (Heinrich and Giisten,1980). Cyclopenta[crf]pyrene, however, does not fluoresce. 

In Fig. 7 we show all Kekule valence structures of benzo[ghi]perylene and their degrees of freedom. The first eight structures have df = 3, the next five Kekule valence structures have df = 2, and the last Kekule valence structure has df = I. The individual Kekule valence structures have quite different count of conjugated circuits R, which can be as high as five (in the first Kekule valence structure) and as low as one (in the last Kekule valence structures). A close look at these... 

In Fig. 9 we illustrate all 1-sextets for benzo[ghi]perylene. Under each structure are the labels indicated the Kekule valence structures involved. In all there are twelve 1-sextet structures to be used in the next step for construction of 2-sextet structures shown in Fig. 10. The first... 

All distinct 2-sextet structures of benzo[ghi]perylene obtained by pair-wise superposition of 1-sextet structures... 

We have inserted in their definition the word uniquely for added precision. In other words, once the positions of inscribed circles have been selected the rest of the molecule should have the residual degree of freedom equal one, that is, positions of all CC double bonds are unique. In Fig. 14 we illustrate the five HH-Clar structures of benzo[ghi]perylene. In the case of benzo[ghi]perylene the first structure is the proper Clar structure that has the maximal number of Jt-sextets. Of the four generalized HH-Clar structures three have two it-sextet and one has but a single Jt-sextet. 

In practice, we have utilized it for the analysis of molecular systems comprised of 3 to 5 fused benzene rings. Our discussion in this document is limited to the following compounds phenanthrene, anthracene, fluoranthene, pyrene, benz(a)anthracene, chrysene, benzo(e)pyrene, benzo(a)pyrene, and dibenz(a,h)anthracene. The structures for these compounds are presented in Table I. It is important to note that the method has also been adapted to the determination of several other PAH compounds (e.g., benzo(c)phenanthrene, perylene, 3-methylcholanthrene, carbazole, 7H-dibenzo(c,g)carbazole, and indeno(l,2,3-cd)pyrene). 

Figure 2 Structures of polycyclic aromatic hydrocarbons. Symbols used in this figure and text Na (naphthalene). Ay (acetonaphthylene), Ae (acenaphthene), FI (fluorene). Pa (phenanthrene), A (anthracene), MPa (methyl phenanthrene), F (fluoranthene), Py (pyrene), BaA (benz(a)anthracene), Chy (chrysene), BlcF (benzo(k)fluoranthene), BbF (benzo(b)fluoranthene), BaP (benzo(a)pyrene), IP (indenopyrene), B(ghi)Pe (benzo(ghi)perylene), and Db(ah)A...

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. 

Being interested here in the volatile components of coffee aroma, we shall arbitrarily limit the list of the aromatic hydrocarbons to tricyclic structures. The higher fused polycyclic hydrocarbons (fluoranthene [206-44-0], pyrene [129-00-0], chrysene [218-01-9], benz[ ]anthracene (1,2-benzanthracene) [56-55-3], benz[< ]acephenanthrylene (3,4-benzofluoranthene) [205-99-2], benzo[ ]pyrene (3,4-benzopyrene, 3,4-BP) [50-32-8], benzo[e]pyrene (1,2-benzopyrene) [192-97-2], perylene [198-55-0], benzo[g,/i,/]perylene (1,12-benzopyrene) [191-24-2], and dibenz[ ,//]anthracene (1,2,5,6-dibenzanthracene) [53-70-3]) cannot be considered as a part of the aroma. However, as some of these, specially benzo[o pyrene, are known for carcinogenic properties, they have been particularly analyzed in food subject to roasting or smoke-curing. 

Figure 26 illustrates the most similar pairs of benzenoids having perimeter P = 18. The similarity ofbenzo[c]phenanthrene (4)-triphenylene (5) and benzanthracene (2)-chrysene (3) was mentioned earlier benzanthracene (2)-benzo[a]pyrene (6) are another such pair the similarity of which is apparent from visual inspection. However, the high similarity of [interatomic separations, the descriptor that is critical in calculating their profiles. Hence, the most similar structures need not necessarily show apparent similarity. This is not the failure of the approach or the failure of the characterization of molecules but is a consequence of difficulties in separating different criteria when comparing structures. Our visual comparison is more likely to capture details of the contours of the molecule rather than an intrinsic property such as the interatomic separations. 

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.

There is very little information available in the literature on the toxicity of this compound. Benzo[g,/2,i]perylene has low oral toxicity. On the basis of its structural similarities with other carcinogenic polynuclear aromatics, this compound is expected to show... 

Benzo(g, h, i) perylene, BghiP, is a five-membered fused phenyl ring PAH of molecular weight 277 and could be considered quite nonpolar. Its molecular structure is as follows ... 

FIGURE 2.10 Calculation of Kekule valence structures for benzo[ /ii]perylene using the method of John and Sachs. 

In Figure 15 we show all 14 Kekule valence structures of benzo[ / i]perylene. A close look at the Kekule valence structures of benzo /2i]perylene shows that, while some are similar (and some are symmetry-related), others are visibly different. In particular, one can notice a difference between the first Kekule structure, in which five rings out of six, when looked at in isolation, have the Kekule valence structure of benzene, and the last structure, in which only one ring has the Kekule valence structure of benzene. The first structure (structure A in Figure 15), which is the Kekule valence structure with the maximal number of Kekule benzene rings, is known as the Fries structure. In the pre-quantum chem-... 

Figure 15. All 14 Kekule valence structures of benzo[ /2i]-perylene.

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