Polycyclic aromatic hydrocarbons definition

On the macroscopic scale, in most cases, only groups of identities can be identified (isotope mixtures, isoto-pomer mixtures, stereoisomer mixtures). The definition of the analyte depends on the selectivity of the analytical method including sample pretreatment, e.g. extraction (see Fig. 3). In a complex composition sometimes only classes of compounds (e.g. fat, polycyclic aromatic hydrocarbons) are identified. In these cases the analyte is designated as a sum parameter. 

There are indications that pure naphthalene (a constituent of mothballs, which are, by definition, toxic to moths) and alkylnaphthalenes are from three to 10 times more toxic to test animals than are benzene and alkylbenzenes. In addition, and because of the low water solubility of tricyclic and polycyclic (polynuclear) aromatic hydrocarbons (i.e., those aromatic hydrocarbons heavier than naphthalene), these compounds are generally present at very low concentrations in the water-soluble fraction of oil. Therefore, the results of this smdy and others conclude that the soluble aromatics of crude oil (such as benzene, toluene, ethylbenzene, xylenes, and naphthalenes) produce the majority of its toxic effects in the enviromnent. 

Obviously there are some parameters like air-fuel ratio where you can find definite and evident trends, and relate them to PAH emissions. Therefore, regulation of polycyclic aromatics is not necessary since the methods to reduce the emission of carbon monoxide and hydrocarbons by engine modifications and after treatment devices also decrease the PAH emission. 

M. Randic, rc-Electron currents in polycyclic conjugated hydrocarbons of decreasing aromatic character and novel structural definition of aromaticity. Open Org. Chem. J. 5 (Suppl. 1-M2) (2011) 11-26. 

Conjugated circuits play the central role in three rather important topics of polycyclic conjugated hydrocarbons (i) definition and expressions of resonance energy, (ii) generalization of the Hiickel 4n + 2 rule of aromaticity, and (iii) calculation of K electron ring currents. In the next three sections, we will address these three topics. 

Definition A generalized Clar structure of a polycyclic benzenoid hydrocarbon is a valence formula in which one or more aromatic Ji-sextets are inscribed in non-adjacent benzene rings such that the remaining part of the structure, obtained by deletion of benzene rings with sextets, must have a Kekule valence structure. 

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