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Über dieses Buch

In the last hundred years benzenoid hydrocarbons have constantly attracted the attention of both experimental and theoretical chemists. In spite of the fact that some of the basic concepts of the theory of benzenoid hydrocarbons have their origins in the 19th and early 20th century, research in this area is still in vigorous expansion. The present book provides an outline of the most important current theoretical approaches to benzenoids. Emphasis is laid on the recent developments of these theories, which can certainly be characterized as a significant advance. Em­ phasis is also laid on practical applications rather than on "pure" theory. The book assumes only some elementary knowledge of organic and physical chemistry and requires no special mathematical training. Therefore we hope that undergraduate students of chemistry will be able to follow the text without any difficulty. Since organic and physical chemists are nowadays not properly acquaint­ ed lVith the modern theory of benzenoid molecules, we hope that they will find this book both useful and informative. Our book is also aimed at theoretical chemists, especially those concerned with the "topological" features of organic molecules. The authors are indebted to Dr. WERNER SCHMIDT (Ahrensburg, FRG) for valuable discussions. One of the authors (1. G.) thanks the Royal Norwegian Council for Scientific and Industrial Research for financial support during 1988, which enabled him to stay at the University of Trondheim and write the present book. Trondheim, July 1989 Ivan Gutman Sven J. Cyvin Contents Chapter 1 Benzenoid Hydrocarbons .

Inhaltsverzeichnis

Frontmatter

Chapter 1. Benzenoid Hydrocarbons

Abstract
Benzenoid hydrocarbons are condensed polycyclic unsaturated fully conjugated hydrocarbons composed exclusively of six-membered rings. Some of their representatives are depicted in Fig. 1.1.
Ivan Gutman, Sven Josef Cyvin

Chapter 2. Benzenoid Systems

Abstract
Benzenoid systems are geometric figures. They are composed of congruent regular hexagons, arranged according to certain rules.
Ivan Gutman, Sven Josef Cyvin

Chapter 3. Anatomy

Abstract
In this chapter, the most important structural characteristics of benzenoid systems are described and the basic relations between them pointed out. After learning enough about the anatomy of the benzenoid systems, we shall be able to put forward several classification schemes.
Ivan Gutman, Sven Josef Cyvin

Chapter 4. Enumeration

Abstract
By enumeration of benzenoid systems, the counting of all possible non-isomorphic members within a class of benzenoids is understood. Usually, but not always, the number of hexagons (h) is the leading parameter. Thus the enumeration for h = 1,2, 3, 4, etc. is to be executed. Figure 2.1 shows the results of enumerations for h = 2,3, and 4, which account for all possible benzenoid systems with these numbers of hexagons. For larger h values, it is of interest to subdivide the total amount of benzenoids into different classes. In this connection we speak about classification.
Ivan Gutman, Sven Josef Cyvin

Chapter 5. Kekulé Structures

Abstract
It is a wide-spread belief among chemists that Kekulé structures are used only within resonance theory (which, on the other hand, would be an oversimplified version of valence bond theory), and are thus of little or no interest for contemporary theoretical chemistry. In this chapter we try to convince the reader that in reality the situation is somewhat different. Recent work in ab initio valence bond theory (Cooper et al. 1986, Gerratt 1987) shows that the importance of Kekulé structures is much greater than is usually presumed, a fact which was known half a century ago, but eventually neglected by the broader scientific community (Pauling 1987).
Ivan Gutman, Sven Josef Cyvin

Chapter 6. Conjugated Circuits

Abstract
In Chapter 3 we saw that the mathematical object corresponding to a Kekulé structure is the 1-factor. The theory of 1-factors is well elaborated (Lovász and Plummer 1986), and in this field numerous mathematical results have been established. In this section we quote some of them, in particular those which provide the basis of the conjugated circuit model.
Ivan Gutman, Sven Josef Cyvin

Chapter 7. Aromatic Sextets

Abstract
The exceptional stability of benzene has long puzzled the organic chemists, and several more or less plausible explanations of this fact have been offered. After the first rough ideas about the electronic structure of molecules had been achieved in the first decades of this century, it became clear that the stability of benzene can be associated with the occurrence of a stable electronic configuration which is a result of the cyclic arrangement of six electrons.
Ivan Gutman, Sven Josef Cyvin

Chapter 8. Coronoids

Abstract
In this chapter we outline the theory of coronoid hydrocarbons (chemical objects) and the related coronoid systems (mathematical objects). As it will be explained in more detail in the following, the coronoids can be viewed as a sort of benzenoids with holes. Thus the class of coronoids represents a proper extension of the class of benzenoids.
Ivan Gutman, Sven Josef Cyvin

Chapter 9. Back to Chemistry

Abstract
There is no doubt that the knowledge of the thermodynamic data for benzenoid hydrocarbons is of prime importance for the understanding of their basic physical and chemical properties and, in particular, their formation in high-temperature processes. Furthermore, thermodynamic parameters are needed for testing the great many resonance energies which are the outcomes of various theoretical approaches to benzenoid molecules (some of which are outlined in Chapters 5, 6, and 7).
Ivan Gutman, Sven Josef Cyvin

Backmatter

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