Polycyclic aromatic compounds definitions

All possible interactions between the K and L groups were taken into account and Akk = 0. The definition contains a minimum number of groups and is satisfactory for most of the binary systems studied. However, it cannot take into account the structural differences which exist between position isomers. This is the case of polycyclic aromatic compounds presenting cycle position isomers or substitute position isomers. Structural differences of this type determine the gaps between the values of certain thermophysical properties of isomers, such as, for example, the fusion temperature or sublimation enthalpy. The further the temperature falls, the more these differences are accentuated. The representation of the solid-fluid (low temperature) equilibria is consequently more difficult and the model must take into account the existing structural differences. We came across this problem in the compounds such as anthracene, phenanthrene, pyrene, methylated naphthalenes, hexamethylbenzene and triphenylmethane. As it was out of the question to increase the number of groups because... 

On the basis of the reaction of alkyl radicals with a number of polycyclic aromatics, Szwarc and Binks calculated the relative selectivities of several radicals methyl, 1 (by definition) ethyl, 1.0 n-propyl, 1.0 trichloromethyl, 1.8. The relative reactivities of the three alkyl radicals toward aromatics therefore appears to be the same. On the other hand, quinoline (the only heterocyclic compound so far examined in reactions with alkyl radicals other than methyl) shows a steady increase in its reactivity toward methyl, ethyl, and n-propyl radicals. This would suggest that the nucleophilic character of the alkyl radicals increases in the order Me < Et < n-Pr, and that the selectivity of the radical as defined by Szwarc is not necessarily a measure of its polar character. 

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. 

From the synthetic point of view, oxidative photocyclization of these two types of enamides has a definite advantage in the construction of a polycyclic ring system with a double bond at the ring juncture in one step from the starting compounds. The photocyclized product can be readily converted to the cis-fused ring system by a facile catalytic reduction or to the fully aromatized lactam on dehydrogenolysis (19,20) as in the case of vV-benzoy-lenamines. 

The described definitions have been widely used to characterize aromaticity. However, the correlation between these criteria and aromatic (or antiaromatic) nature is by no means simple. Even more so, the aromatic character is, by definition, a relative property, namely, one can assign aromaticity only by referring to model compounds. Thus, even when the number of 71-electrons calls for the existence of aromatic character, its extent cannot be predicted. Similarly the relationship between magnetic susceptibility of a polycycle and its conjugative stabilization is highly complex 105,106). 

The aceheptylene 23 is a system of 14 carbon atoms of which 13 carbons compose its conjugated periphery. Accordingly, 23 can be considered as a perturbed [13] an-nulene or as a (4n + 1 )tc conjugated system (n = 3) with an inner carbon atom. This system seems most suitable to examine the basic problem of patterns of delocalization in polycyclic anions. In view of the mentioned Platt s peripheral definition 87) such a compound is expected to be a noparomatic polyvinylic system, not exhibiting any aromatic or antiaromatic properties. This expectation is unambiguously confirmed. 

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