Qualitative Valence-Bond Descriptions of Electron-Rich Molecules: Pauling “3-Electron Bonds” and “Increased-Valence” Theory : Pauling '3-Electron Bonds' and 'Increased-Valence' Theory

This book provides qualitative molecular orbital and valence-bond descriptions of the electronic structures for electron-rich molecules, with strong emphasis given to the valence-bond approach. Electron-rich molecules form an extremely large class of molecules, and the results of quantum mechanical studies from different laboratories indicate that qualitative valence-bond descriptions for many of these molecules are incomplete in so far as they usually omit "long-bond" Lewis structures from elementary descriptions of bonding. For example, the usual representation for the electronic structure of the ground-state for 03 involves resonance between the (+1 o and Until standard Lewis structures ~ ~ (-I . b:'" ~d· . . . . , recently, any contribution to resonance of the "long-bond" (or spin-paired o •• / •• ,. . has been largely ignored. diradica~ Lewis structure However, it :0 . 0. . e-. . . . . \_\_\_\_\_\_ " has now been calculated to be a very important structure. For the ground-states of numerous other systems, calculations also indicate that "long-bond" structures are more important than is usually supposed, and therefore they should frequently be included in qualitative valence-bond descriptions of electronic structure. The book describes how this may be done, and some of the resulting consequences for the interpretation of the electronic structure, bond properties and reactivities of various electron-rich molecules. When appropriate, molecular orbital and valence­ bond descriptions of bonding are compared, and relationships that exist between them are derived. Front Matter....Pages N2-X Atomic Orbitals, Electron Spin, Linear Combinations....Pages 1-8 Pauling “3-Electron Bonds”, 4-Electron 3-Centre Bonding, and the Need for an “Increased Valence” Theory....Pages 9-30 Wave-Functions and Valence-Bond Structures for 1-Electron Bonds, Electron-Pair Bonds, Pauling “3-Electron Bonds” and “No Bonds”....Pages 31-47 Valence-Bond Structures for Some Diatomic Molecules....Pages 48-54 Pauling “3-Electron Bonds” and Hypoligated Transition Metal Complexes....Pages 55-62 Pauling “3-Electron Bonds”, 5-Electron 3-Centre Bonding and Some Tetra-Atomic Radicals....Pages 63-72 Some Dimers of Triatomic Radicals with 17 and 19 Valence-Shell Electrons....Pages 73-87 Some Cu(II) Binuclear Transition-Metal Complexes....Pages 88-99 Excited States....Pages 100-107 Pauling “3-Electron Bonds” and “Increased Valence” Theory for N 2 O 4 ....Pages 108-113 Pauling “3-Electron Bonds” and “Increased-Valence” Structures....Pages 114-135 Increased-Valence Structures Constructed from Lewis Structures: Delocalization of Lone-Pair Electrons into Vacant Bonding Orbitals....Pages 136-139 “Increased-Valence” Structures for N -Centre Bonding Units....Pages 140-160 Delocalization of Lone-Pair Electrons into Antibonding Orbitals: Increased-Valence Structures, Molecular Orbital Theory and Atomic Valencies....Pages 161-170 Slater Determinants and Wave-Functions for “Increased-Valence” Structures....Pages 171-175 Classical Valence Structures and Quinquevalent Nitrogen Atoms....Pages 176-181 Some Tetrahedral Molecules and d π − P π Bonding for Some Sulphur Compounds....Pages 182-192 Transition Metal Complexes with CO, N 2 , NO and O 2 Ligands....Pages 193-205 Some Electron-Excess σ Bonded Systems....Pages 206-216 Intermolecular Donor-Acceptor Complexes....Pages 217-224 Base-Displacement Reactions and Electron Conduction in Alkali Metals....Pages 225-231 Free-Radical and Spin-Paired Diradical Reactions....Pages 232-244 Some Comparisons of Types of Wave-Functions for 4-Electron 3-Centre Bonding Units....Pages 245-255 A Note on Pauling “3-Electron Bonds” and Covalent-Ionic Resonance....Pages 256-258 Back Matter....Pages 259-260 This book provides qualitative molecular orbital and valence-bond descriptions of the electronic structures for electron-rich molecules, with strong emphasis given to the valence-bond approach. Electron-rich molecules form an extremely large class of molecules, and the results of quantum mechanical studies from different laboratories indicate that qualitative valence-bond descriptions for many of these molecules are incomplete in so far as they usually omit "long-bond" Lewis structures from elementary descriptions of bonding. For example, the usual representation for the electronic structure of the ground-state for 03 involves resonance between the (+1 o and Until standard Lewis structures ~ ~ ( -I . b:'" ~d· ..., recently, any contribution to resonance of the "long-bond" (or spin-paired o " / ", . . has been largely ignored. diradica~ Lewis structure However, it :0 . 0. . e-. ... ______ " has now been calculated to be a very important structure. For the ground-states of numerous other systems, calculations also indicate that "long-bond" structures are more important than is usually supposed, and therefore they should frequently be included in qualitative valence-bond descriptions of electronic structure. The book describes how this may be done, and some of the resulting consequences for the interpretation of the electronic structure, bond properties and reactivities of various electron-rich molecules. When appropriate, molecular orbital and valenceƯ bond descriptions of bonding are compared, and relationships that exist between them are derived