"The second step is to determine constitution, Le. which atoms are bonded to which and by what types of bond. The result is ex pressed by a planar graph (or the corresponding connectivity mat rix) In constitutional formulae, the atoms are represented by letters and the bonds by lines. They describe the topology of the molecule." VLADIMIR PRELOG, Nobel Lecture, December l2;h 1975. In the present notes we describe the topological approach to the che mistry of conjugated molecules using graph-theoretical concepts. Con jugatedstructures may be conveniently studied using planar and connec ted graphs because they reflect in the simple way the connectivity of their pi-centers. Connectivity is important topological property of a molecule which allows a conceptual qualitative understanding, via a non numerical analysis, of many chemical phenomena or at least that part of phenomenon which depends on topology. This would not be possible sole ly by means of numerical (molecular orbital) analysis.
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ISBN-13
978-3-642-93069-0 (9783642930690)
DOI
10.1007/978-3-642-93069-0
Schweitzer Klassifikation
1. Introduction.- 2. Graphs in Chemistry.- 2.1. Basic Definitions and Concepts of Graph Theory.- 2.2. Graphs and Topology.- 2.3. Graphs Representing Conjugated Molecules.- 2.4. Graph Spectrum. Sachs Theorem.- 2.5. Topology and Simple Molecular Orbital Model.- 2.6. Application of the Coulson-Sachs Graphical Method.- 2.7. Extension of Graph-Theoretical Considerations to Möbius Structures.- 3. Total Pi-Electron Energy.- 3.1. Introduction.- 3.2. Identities And Inequalities.- 3.3. The Coulson Integral Formula.- 3.4. Topological Factors Determining the Gross Part of Epi.- 3.5. The Influence of Cycles: The Hückel Rule.- 3.6. The Influence of KekulÉ Structures.- 3.7. The Influence of Branching.- 3.8. Summary.- 4. Resonance Energy.- 4.1. Introduction.- 4.2. Classical and Dewar Resonance Energies.- 4.3. Topological Resonance Energy.- 4.4. Tre as a Criterion of Aromatic Stability. Correlation with Experimental Findings.- 4.5. Concluding Remarks.- 5. Reactivity of Conjugated Structures.- 5.1. Localization Energy.- 5.2. Dewar Number.- 5.3. Topological Approach to Localization Energy.- 5.4. Topological Aspect of Dewar Number.- 5.5. Nonbonding Molecular Orbitals.- 6. Conclusions.- 7. Literature.
