Picene, structure

A set of n = 209 polycyclic aromatic compounds (PAC) was used in this example. The chemical structures have been drawn manually by a structure editor software approximate 3D-structures including all H-atoms have been made by software Corina (Corina 2004), and software Dragon, version 5.3 (Dragon 2004), has been applied to compute 1630 molecular descriptors. These descriptors cover a great diversity of chemical structures and therefore many descriptors are irrelevant for a selected class of compounds as the PACs in this example. By a simple variable selection, descriptors which are constant or almost constant (all but a maximum of five values constant), and descriptors with a correlation coefficient >0.95 to another descriptor have been eliminated. The resulting m = 467 descriptors have been used as x-variables. The y-variable to be modeled is the Lee retention index (Lee et al. 1979) which is based on the reference values 200, 300, 400, and 500 for the compounds naphthalene, phenanthrene, chrysene, and picene, respectively. 

A more striking case which illustrates the advantage of the equivalent alternative forms was discovered sometime ago by one of the authors [33] An alternative form of a KekulS valence-bond structure, K, is its factor graph, F(K), c f Fig 4 In Fig 6 all Kekul structures of picene are hown (in the form of their Clar notation) along with the corresponding factor graphs One recalls that an F(K) is... 

In addition, the occurrence of picene derivatives as well as similar polynuclear aromatic systems (White, 1983) in the solvent extracts of coal might be cited as evidence for the inclusion of sterane-type materials in the precursor material to coal. This does assume that the skeletal structure remains intact throughout the maturation process and that there has been no degradation or even formation of new skeletal systems. Indeed, the biosynthesis of aromatic compounds is well documented, including the synthesis of aromatic species from nonaromatic precursors (Weiss and Edwards, 1980 Lee et al., 1981). 

The photodehydrocyclization reaction was employed to produce 14,15-diphenyldibenzo[fJ]picene (93) (Fig. 28) in 0.8% yield [85]. The mass and NMR spectra were used to support the structure assignment. 

The structure of l,8-dimethyl-as-indaceno[3,2,l,8,7,6-p rimv]picene (157a) was analyzed by X-ray crystallography [168]. The maximum POAV pyramidalization angle was determined to be 8.4°, slightly greater than that of corannulene (8.2°). 

Kekule valence stractures. One can easily see that the number of Kekule valence structures depends on the positioning of kink rings and increases with the number of kink rings. Of the six benzenoids of figure 2.5, the largest number of Kekule valence structures has picene, the last benzenoid of Figure 2.5. 

Wang Y, Motta SD, Negri F, Friedlein R (2011) Effect of oxygen on the electronic structure of highly crystalline picene films. J Am Chem Soc 133 10054—10057... 

---