Cata-condensed

The fused 3+ ring aromatics in petroleum include both cata- and peri-condensed stmctures (see Table 4, Fig. 8). The cata-condensed species are those stmctures where only one face is shared between rings, the peri-condensed molecules are those that share more than one face. The fused ring aromatics form the class of compounds known as polynuclear aromatic hydrocarbons (PAH) which includes a number of recognized carcinogens in the 4+ ring family (33). Because of the potential health and environmental impact of PAH, these compounds have been studied extensively in petroleum. 

On the other hand, in cata-condensed nonalternant hydrocarbons IV, VI, X and XI, peri-condensed nonalternant hydrocarbons XIV — XVIII, fulvenes XIX and XX, and fulvalenes XXI—XXIII, self-consistency was achieved only for the fully-symmetrical nuclear arrangement. All these molecule, except azulene pCl), also show in a greater or lesser degree a pronounced double-bond fixation. 

Of the cata-condensed nonalternant hydrocarbons undergoing a pseudo Jahn-Teller distortion, pentalene (I) and heptalene (VII), having the largest value, are predicted to possess a strong bond alternation. This confirms the results of the previous theoretical investi-gations " and agrees with the available experimental facts ... 

Platt JR (1949) Classification of spectra of cata-condensed hydrocarbons. J Chem Phys 17 484... 

Kearns, D. R. Determination of the assignment of triplet states in cata-condensed aromatic hydrocarbons. J. Chem. Phys. 36, 1608 (1962). 

An excised internal structure or insular structure is a structure obtained by excising out the set of connected internal vertices usually associated with a strictly peri-condensed benzenoid hydrocarbon [3,13]. A strictly peri-condensed benzenoid PAH6 has all its internal third degree vertices mutually connected, has no cata-condensed... 

Rank order is increasing from top to bottom and left to right. Fig. 1. Scheme for recursive enumeration of the cata-condensed benzenoids... 

Fig. 3 Cata-condensed benzenoid hydrocarbons with more than one Clar structure...

For coals whose carbon contents are less than 90 weight %, it is reported (15,16) that the condensed aromatic rings are mostly of the cata-condensed type with two through five rings. 

Aromatic condensed rings are of cata-condensed type. 

The nomenclature applicable to cata-condensed (no atom is common to three or more rings) benzenoid (all carbon rings of size 6) molecules comprised of n rings, that are not also corona-condensed (forms a ring of rings) is one of simplicity and organization. Every member of this set has the same principal part in their name ... 

All that is needed to complete the canonical name is to locate the remaining bonds, as well as the location of the hydrogen atoms, by the above described system. For example, Figure 10 illustrates the names of the seven tetrabenzenes (5 cata-condensed, 1 peri-condensed and 1... 

The structural parameter Ham/Car, which gives the ratio of substitutable edge atoms to total aromatic atoms, is important because it is a measure of the average aromatic ring system which is independent of molecular weight measurements. Figure 2 shows the Ham/Car values for some typical 1-7 cata-condensed aromatic ring systems. When the Ham/... 

Figure 2. Comparison of Haru/ ar values for cata-condensed aromatic...

Figure 2.8 shows how the experimentally observed wavelengths for two series of cata-condensed benzenoid hydrocarbons, the linearly annelated acenes and the angularly annelated phenes, change with increasing number of benzene rings. The shifts in the Lb and Bb positions are parallel to one another in both series, whereas the bathochromic shift of the Lj, band of acenes upon annelation is so pronounced that even in anthracene it masks the Lb band. 

Moffitt, W. (1954), The Electronic Spectra of Cata-Condensed Hydrocarbons, J. Chem. Phys. 72,320. 

Dobrynin, A.A. (1998b). New Congruence Relations for the Wiener Index of Cata-Condensed Benzenoid Graphs. J.Chem.lnf.Comput.Sci.,38,405-409. 

John, P.E., Malhon, R.B. and Gutman, I. (1998). An Algorithm for Counting Spanning Trees in Labeled Molecular Graphs Homeomorphic to Cata-Condensed Systems. J.Chem.Inf Corn-put. ScL, 38,108-112. 

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