Compounds with Polycyclic Molecular Structures

The carcinogenicity of polycyclic aromatic compound-rich tyre extender oils has lead to the proposal of a legislative ban on their use in Europe. The suitability of naphthenic oils as non-toxic plasticisers in tyre treads is discussed and results are presented of experimental studies of the use of these plasticisers in SBR, EPDM, sulphur-cured EPDM and peroxide-cured EPDM. Despite their low aromatic content, the naphthenic plasticisers are shown to give good results in SBR, probably as a result of the contribution to solvent characteristics of the naphthenic molecular structure. The use of naphthenic oils is expected to increase worldwide as they are said to be one of the best alternatives to aromatic extracts with regard to solvent properties, compatibility, performance and availability. 

Detailed analysis of residual products, such as residual fuel oil, is more complex than the analysis of lower-molecular-weight liquid products. As with other products, there are a variety of physical property measurements that are required to determine that residnal fnel oil meets specifications. But the range of molecular types present in petrolenm prodncts increases significantly with an increase in the molecular weight (i.e., an increase in the number of carbon atoms per molecule). Therefore, characterization measurements or studies cannot, and do not, focus on the identification of specific molecular structures. The focus tends to be on molecular classes (paraffins, naphthenes, aromatics, polycyclic compounds, and polar compounds). 

Polycyclic arenes, e.g. perylene, have been widely studied in the preparation of molecular conductors, some of the radical cations show semiconducting or metallic behavior [418]. Introduction of one or more sulfur atoms at the periphery of such systems, i.e. thia arene derivatives, generally imparts greater stability to the radical-cation salts, coupled with increase conductivity [419]. For compound 116, X-ray structure studied have been reported on the pure donor and some radical-ion salts [420]. 

He L, Jurs PC, Custer LL, Durham SK, Pearl GM. Predicting the genotoxicity of polycyclic aromatic compounds from molecular structure with different classifiers. Chem Res Toxicol 2003 16 1567-80. 

Condensed polycyclic benzenoid aromatic hydrocarbons are customarily regarded as planar molecular structures because of the geometrical constraints of carbon atoms in a state of sp2 hybridization. A well-known exception is the class of compounds called the helicenes (18) for which the nonbonded overlap of two terminal benzenoid rings in a cata-condensed structure, as in structure 1, forces a molecule into a nonplanar helical structure. A second exceptional class of compounds is related to corannulene (2) and other an-nulenes of this type (19, 20). In corannulene, strain associated with the pericondensed five- and six-membered rings requires adoption of a bowlshaped structure (20, 21). For both structures 1 and 2 the aromatic character of the benzenoid rings is retained to an appreciable extent. 

Single-boundary three-dimensional aromatic hydrocarbons do have high photoconductivities (41), but the relationship between molecular structure and photoconductivity remains unclear. In this regard, the red shift of structure 4 in comparison with the presumably planar parent compound, namely tetrabenz[a,c,/i,j]anthracene (24) may be significant. In this book, Fetzer (15) gives UV-visible spectra for these kinds of polycyclic aromatic com-... 

The in-tube SPME method is suitable for the extraction of less volatile or thermally labile HCAs compounds [89]. The food sample is treated with HCl followed by centrifugation, the sample supernatant is neutralized with NaOH, and the HCAs are extracted by the Blue Rayon adsorption method. This method can selectively adsorb compounds having polycyclic planar molecular structures, such as HCAs, in order to concentrate them from the aqueous solution. The extract is passed through a syringe micro filter, and a capillary colunm is used as a SPME device. This column is placed between the injection loop and the injection needle of the auto sampler. The method is simple, rapid, automatic, and gives 3-20 times higher sensitivity in comparison with the direct liquid injection method [89]. 

Motivated by the requirement of analysis and separation of polycyclic aromatic hydrocarbons, several authors have determined the retention indices of some of these compounds in chromatographic columns. Since the retention indices of many polycyclic aromatic hydrocarbons have not been determined yet, it is desirable to find the mathematical model about the relationships between the value of retention indices and molecular structure of polycyclic aromatic hydrocarbons. Some of these relationships have been studied by PLS. But it can be shown that support vector machine can give mathematical model with better prediction ability. Table 13.3 illustrates the experimental values of 33 polycyclic aromatic hydrocarbons and their molecular parameters [52 5]. Support vector regression has been used for this modeling work. 

---