The Donor-Acceptor Approach to Molecular Interactions

Recent developments in various areas of chemistry have been decisively influenced by the principles of structure and mechanism and by the ideas of coordination chemistry, in particular by the donor-acceptor approach, A unified view of almost all kinds of molecular forces is provided by quantum mechanics, and for practical purposes have been classified according to model assumptions, namely, dispersion, polarization, electrostatic, and short-range forces. The latter are divided into two- and three-center covalent chemical bonds, metallic bonds, and exchange-repulsion forces. This approach allows statements of principle and systematic analysis. However, quantitative predictions on concrete large systems are virtually impossible, and there are no general rules that account for structural and chemical changes due to intermolecular interactions. Chemists are therefore left with qualitative descriptions in which the changes in electron densities are considered. Such models as the MO theory or the resonance concept unrealistically assume that the nuclei remain in fixed positions. Further difficulties are encountered in the attempted description on the "nature" of the chemical bond, e.g., the forces involved. In order to avoid these difficulties an extension of the donor-acceptor concept, characterized by the comparison between equilibrium structures in different molecular environments, will be presented in this book. In this way, changes in the positions of the nuclei can be taken into account and the question of the nature of the molecular forces is no longer important.

1. Basic Considerations.- 1.1. Introduction.- 1.2. Charge-Density Rearrangement Caused by an Intermolecular Interaction.- 1.3. The First Bond-Length Variation Rule.- 1.4. The Second Bond-Length Variation Rule.- 1.5. The Third Bond-Length Variation Rule.- 1.6. General Aspects.- 2. Empirical Parameters for Donor and Acceptor Properties.- 2.1. Solvent Characterization by Empirical Parameters.- 2.2. The Donor Number.- 2.3. The Acceptor Number.- 3. Molecular Adducts.- 3.1. Theoretical Approaches.- 3.2. Application of the Bond-Length Variation Rules.- 3.3. Application of the Empirical Parameters.- 3.4. Metal Carbonyls and Related Compounds.- 3.5. Molecular Adducts of Organic Carbonyl Compounds and of Phenols.- 4. Bond-Length Considerations in the Crystalline State.- 4.1. Molecular Lattices.- 4.2. Ionic Crystals.- 4.3. Silicates.- 4.4. Bond-Length Variability in Complex Compounds.- 4.5. Bond-Length Variations under Pressure.- 5. Interface Phenomena.- 5.1. Lattice Contraction at Clean Crystal Surfaces.- 5.2. Crystal Size and Lattice Deformation.- 5.3. Adsorption Phenomena.- 5.4. Surface Layers.- 5.5. Epitaxy Phenomena.- 5.6. Solid-Water Interfaces.- 5.7. Other Surface Phenomena.- 5.8. Crystal Growth.- 6. Molecular Association in the Liquid State.- 6.1. Association by Hydrogen Bonds.- 6.2. Liquid Water and Its Solutions.- 6.3. Association in Aprotic Liquids.- 7. Ion Solvation.- 7.1. General Considerations.- 7.2. Relationships between Thermodynamic Solvent Transfer Quantities and Empirical Solvent Parameters.- 7.3. Charge-Density Rearrangement by Ion Solvation.- 7.4. Outer-Sphere Effects in Cation Solvation.- 7.5. Outer-Sphere Effects in Anion Solvation.- 8. Redox Properties.- 8.1. Solvent Effects.- 8.2. Ligand Effects.- 9. Solvation in Solvent Mixtures.- 9.1. Preferential Solvation.- 9.2. Solvent-Solvent Interactions.- 9.3. Homoselective and Heteroselective Solvation.- 10. Ionization Equilibria.- 10.1. Heterolysis by Coordinating Interactions.- 10.2. Heterolysis by Redox Interactions.- 10.3. Homolytic and Heterolytic Dissociation Energy.- 10.4. Solvent-Separated Ion Pairs: The Role of the Dielectric Constant.- 10.5. Outer-Sphere Ion Association.- 10.6. The Concept of Contact Ion Pairs.- 10.7. A Simplified Reaction Scheme.- 11. Complex Stabilities in Solution.- 11.1. Qualitative Considerations.- 11.2. Quantitative Considerations.- 11.3. Autocomplex Formation.- 11.4. Solubility Considerations.- 12. Kinetics of Substitution Reactions.- 12.1. General Considerations.- 12.2. Substitution at Carbon.- 12.3. Substitution at Metal Complexes.- 12.4. Outer-Sphere Effects.- 13. Kinetics of Redox Reactions of Metal Complexes.- 13.1. General Considerations.- 13.2. Outer-Sphere Mechanism.- 13.3. Inner-Sphere Mechanism.- 14. Solvent and Reaction Effects on the Course of Substitution and Insertion Reactions.- 14.1. General Considerations.- 14.2. Reactions Involving Organo-Alkali Metal Compounds.- 14.3. Grignard Reactions.- 14.4. Reactions of Carbon Dioxide.- 14.5. Reactions of Molecular Nitrogen.- 14.6. Reactions of Silicon Compounds.- 14.7. Reactions of Boron Compounds.- 15. Miscellaneous Applications.- 15.1. Outer-Sphere Effects on Oxo Anions.- 15.2. Molten Salts.- 15.3. Liquid-Liquid Extraction.- 15.4. Stabilization of Colloids in Liquid Dispersion Media.- 15.5. Solvent Effects on Electronic Spectra.- 16. Homogeneous and Heterogeneous Catalysis.- 16.1. Catalytic Ability.- 16.2. Catalytic Selectivity in Homogeneous Catalysis.- 16.3. Catalytic Selectivity in Heterogeneous Catalysis.- 16.4. Elimination Reactions on Solid Catalysts.- 16.5. Addition of Hydrogen Halides to Alkenes on Solid Catalysts.- 17. Biochemical Applications.- 17.1. General Considerations.- 17.2. Remarks on the Role of Water in Biological Systems.- 17.3. Oxidation of Hemoglobin.- 17.4. Carbonic Anhydrase.- 17.5. Corrinoids.- 17.6. Activation of Phosphate Transfer.- References.