scholarly journals Valence Bond Theory—Its Birth, Struggles with Molecular Orbital Theory, Its Present State and Future Prospects

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1624
Author(s):  
Sason Shaik ◽  
David Danovich ◽  
Philippe C. Hiberty
Keyword(s):  
Molecular Orbital ◽  
Present State ◽  
Valence Bond ◽  
Molecular Orbital Theory ◽  
Future Prospects ◽  
Orbital Theory ◽  
Linus Pauling ◽  
Valence Bond Theory ◽  
Bond Theory ◽  
Mo Theory

This essay describes the successive births of valence bond (VB) theory during 1916–1931. The alternative molecular orbital (MO) theory was born in the late 1920s. The presence of two seemingly different descriptions of molecules by the two theories led to struggles between the main proponents, Linus Pauling and Robert Mulliken, and their supporters. Until the 1950s, VB theory was dominant, and then it was eclipsed by MO theory. The struggles will be discussed, as well as the new dawn of VB theory, and its future.

Electronic levels in simple conjugated systems, I. Configuration interaction in cyclobutadiene

1950 ◽  
Vol 202 (1071) ◽  
pp. 498-506 ◽  
Keyword(s):  
Molecular Orbital ◽  
Configuration Interaction ◽  
Energy Levels ◽  
Valence Bond ◽  
Wave Functions ◽  
The Other ◽  
Orbital Theory ◽  
Valence Bond Theory ◽  
Symmetry Properties ◽  
Bond Theory

In the simplest cyclic system of π-electrons, cyclobutadiene, a non-empirical calculation has been made of the effects of configuration interaction within a complete basis of antisymmetric molecular orbital configurations. The molecular orbitals are made up from atomic wave functions and all the interelectron repulsion integrals which arise are included, although those of them which are three- and four-centre integrals are only known approximately. In this system configuration interaction is a large effect with a strongly differential action between states of different symmetry properties. Thus the 1 A 1g state is several electron-volts lower than the lowest configuration of that symmetry, whereas for 1 B 1g the comparable figure is about one-tenth of an electron-volt. The other two states examined, 1 B 2g and 3 A 2g are affected by intermediate amounts. The result is a drastic change in the energy-level scheme compared with that based on configuration wave functions. Neither the valence-bond theory nor the molecular orbital theory (in which the four states have the same energy) gives a satisfactory account of the energy levels according to these results. One conclusion from the valence-bond theory which is, however, confirmed, is the somewhat unexpected one that the non-totally symmetrical 1 B 2g state is more stable than the totally symmetrical 1 A 1g . On the other hand, it is clear that the valence-bond theory, with the usual value for its exchange integral, grossly exaggerates the resonance splitting of the states, giving separations between them several times too great. Thus the valence-bond theory leads to large values of the resonance energy (larger, per π-electron, than in benzene) and so associates with the molecule a considerable π-electron stabilization. This expectation has no support in the present more detailed and non-empirical calculations.

The molecular orbital theory of chemical valency XIII. Orbital wave functions for excited states of a homonuclear diatomic molecule

1953 ◽  
Vol 216 (1126) ◽  
pp. 424-433 ◽  
Keyword(s):  
Molecular Orbital ◽  
Excited States ◽  
Valence Bond ◽  
Present Theory ◽  
Wave Functions ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Bond Theory ◽  
Homonuclear Diatomic Molecules ◽  
Approximate Wave

The expansions for the exact wave functions for excited states of homonuclear diatomic molecules derived in part XII are used as the basis for discussing various approximate wave functions of the orbital type. The states considered in detail are the lowest states of symmetries 1 Σ u + , 3 Σ u + . The calculus of variations is used to determine the optimum forms for the component orbital functions. A transformation to equivalent orbitals is used to bring out the physical significance of the various wave functions, and to relate the present theory to earlier theories, in particular the molecular orbital theory, the valence-bond theory and their generalizations.

Chemical Bonding 2: Modern Theories of Chemical Bonding

2021 ◽  
pp. 102-128
Author(s):  
Christopher O. Oriakhi
Keyword(s):  
Chemical Bonding ◽  
Valence Bond ◽  
Molecular Geometry ◽  
Electron Delocalization ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Valence Bond Theory ◽  
Electron Group ◽  
Bond Theory ◽  
Lewis Structures

Chemical Bonding II: Modern Theories of Chemical Bonding explains four bonding theories related to molecular geometry and bonding. Lewis structures and the Valence-Shell Electron-Pair Repulsion (VSEPR) model are used to describe and predict the electron group geometry, molecular geometry and shapes of molecules. The VSEPR model is then used to predict molecular polarity as a function of shape. This leads to Valence Bond Theory, which uses the principles of orbital overlap and hybridization of atomic orbitals to describe chemical bonding. Finally the Molecular Orbital Theory (MOT) based on electron delocalization is discussed in terms of bonding and anti-bonding molecular orbitals.

scholarly journals Analysis of One-Bond Se-Se Nuclear Couplings in Diselenides and 1,2-Diselenoles on the Basis of Molecular Orbital Theory: Torsional Angular Dependence, Electron Density Influence, and Origin inJ1(Se, Se)

2009 ◽  
Vol 2009 ◽  
pp. 1-9 ◽  
Author(s):  
Akito Tanioku ◽  
Satoko Hayashi ◽  
Waro Nakanishi
Keyword(s):  
Electron Density ◽  
Molecular Orbital ◽  
Angular Dependence ◽  
Basis Sets ◽  
Molecular Orbital Theory ◽  
Spin Orbit ◽  
Slater Type ◽  
Orbital Theory ◽  
Derivatives Of ◽  
Mo Theory

Nuclear couplings for the Se-Se bonds,J1(Se, Se), are analyzed on the basis of the molecular orbital (MO) theory. The values are calculated by employing the tripleζbasis sets of the Slater type at the DFT level.J1(Se, Se)are calculated modeled by MeSeSeMe (1a), which shows the typical torsional angular dependence onϕ(CMeSeSeCMe). The dependence explains well the observedJ1(Se, Se)obsdof small values (≤64 Hz) forRSeSeR′(1) (simple derivatives of1a) and large values (330–380 Hz) observed for 4-substituted naphto[1,8-c,d]-1,2-diselenoles (2) which correspond tosymperiplanardiselenides.J1(Se, Se :2) becomes larger as the electron density on Se increases. The paramagnetic spin-orbit terms contribute predominantly. The contributions are evaluated separately from each MO(ψi)and eachψi→ψatransition, whereψiandψaare occupied and unoccupied MO's, respectively. The separate evaluation enables us to recognize and visualize the origin and the mechanism of the couplings.

Sign in / Sign up

Export Citation Format

Share Document