Benzenoids cata-condensed

Nomenclature of Benzenoid Cata-Condensed Polycyclic Aromatic Hydrocarbons. 

A. T. Balaban and F. Harary, Chemical graphs V. Enumeration and proposed nomenclature of benzenoid cata-condensed polycyclic aromatic hydrocarbons. Tetrahedron 24 (1968) 2505-2516. 

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...

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 ... 

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. 

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

Balaban, A.T. (1969) Chemical graphs. VII. Proposed nomenclature of branched cata-condensed benzenoid polycyclic hydrocarbons. Tetrahedron, 25, 2949-2956. 

Aromaticity. VIII). Resonance energies of cata-condensed benzenoid polycyclic hydrocarbons. Rev. Roum. Chim., 15, 1243—1250. 

Dobrynin, A.A. (1998b) New congruence relations for the Wiener index of cata-condensed benzenoid graphs. J. Chem. Inf. Comput. Sci., 38, 405—409. 

The role of Young diagrams in the ordering of chemical structures is explained by their relation to alkane hydrocarbons and unbranched cata-condensed benzenoid systems. 

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. 

Figure 5. Caterpillar graphs representing resonance pattern for n-sextets for several cata-condensed benzenoid hydrocarbons.

The Molecular Profiles for Selected cata-Condensed Benzenoids (Shown in Figure 27)... 

In the former only the carbon atoms on the molecular periphery contribute in the construction of the average interatomic distances and the average powers of the distances. For cata-condensed benzenoids, both and S are identical, but for peri-condensed benzenoids there is a difference between the two sets of descriptors. When we use 5 descriptors in the regressions of the Chromatographic retention indices we obtain ... 

Although the alkane and alkane-like substances are the most important, no series of compounds has received as much interest in generating isomer series as has the polyhexes, with much being done on various classes of benze-noids. For example, isomer series are available for benzenoids of a variety of classes, including peri-condensed, cata-condensed, essentially disconnected,helicenes, ° resonant sextets, quinones, coronenes, "" and pyrenes.Recently, with the aid of a new lattice... 

We first consider the numeric Kekule structures of cata-condensed benzenoids. As an example, we consider dibenzo[b, ]phenanthrene. In Fig. 9.14 we give geometric Kekule stmctures of dibenzo[b,g]phenanthrene and in Fig. 9.15 their numeric counterparts. Kekule structures of dibenzo[b,g]phenanthrene can be generated in... 

From the numbers coding the numeric Kekule structures of cata-condensed benzenoids, a given Kekule structure can be easily recovered because the number of digits in the code determines the number of hexagons in the cata-condensed benzenoid, and the sum of digits gives the total rc-electron count in the benzenoid. 

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