Titlebook: Kekulé Structures in Benzenoid Hydrocarbons; S. J. Cyvin,I. Gutman Book 1988 Springer-Verlag Berlin Heidelberg 1988 Combinatorics.algorith

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Benzenoid Systems: Basic Concepts,procedure, it is beneficial to seek for an appropriate mathematical representation of benzenoid hydrocarbons as well as of Kekulé structures. Fortunately both such mathematical objects are already known in combinatorics. These are the benzenoid systems and the perfect matchings.

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Regular Six-Tier Strips and Related Systems, Some of these formulas have been given more or less sporadically in different connections (Cyvin and Gutman 1986a; Cyvin SJ, Cyvin and Bergan 1986; Gutman and Cyvin 1987b; Cyvin 1987b; Cyvin BN and Cyvin 1987), but a systematic treatment has not been published before.

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Benzenoids with Repeated Units,ins (see, e.g. Fig. 4.9 or CHART 6-II) may be considered as (trivial) benzenoids with repeated units. A less trivial example is the single chain with equal segments in a zigzag arrangement (CHART 6-II). Several typical examples are found among the all-benzenoid classes, both catacondensed (Section 6.5) and pericondensed (Chapter 16).

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Kekulé Structures in Benzenoid Hydrocarbons978-3-662-00892-8Series ISSN 0342-4901 Series E-ISSN 2192-6603

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Introduction,Chemists have been faced with benzenoid hydrocarbons and their derivatives from the earliest days of organic chemistry. These chemical compounds are usually insensitive, stable over long periods of time, available in large amounts and cheap. They can be easily purified and characterized and undergo well understood chemical reactions.

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,Non-Kekuléan and Essentially Disconnected Benzenoid Systems,In the present chapter we outline the basic facts about those benzenoids which are not normal. As already explained in Paragraph 2.3.2 these are the non-Kekuléan systems (for which no Kekulé structure can be drawn) and the essentially disconnected systems (which possess fixed single or double bonds).