Electron Pair Theories

We have not increased the number of electrons at all. All we have done is shared them between the two elements, thereby enabling each atom to have a full outer shell. This approach is known as the electron-pair theory. 

Polyhedral Skeletal Electron Pair Theory The Wade-Mingos Rules... 

Laboratory. During the period 19191922, Langmuir developed what he called a "deductive chemistry" using the electron-pair theory of valency and the quantum hypothesis. However, physicists rejected the premises and methodology of Langmuir s theory, which proposed the existence of a "quantum force" to counterbalance Coulombic attraction and which used the notion of principal quantum number but deduced positions of equilibrium rather than quantum jumps for electrons. 12... 

Kutzelnigg, W. Electron Correlation and Electron Pair Theories. 40, 31—73 (1973). 

The following optimum electron numbers have been defined on the basis of the so-called Polyhedral Skeletal Electron-Pair Theory (PSEPT) . 

During the last decade MO-theory became by far the most well developed quantum mechanical method for numerical calculations on molecules. Small molecules, mainly diatomics, or highly symmetric structures were treated most accurately. Now applicability and limitations of the independent particle, or Hartree-Fock (H. F.), approximation in calculations of molecular properties are well understood. An impressive number of molecular calculations including electron correlation is available today. Around the equilibrium geometries of molecules, electron-pair theories were found to be the most economical for actual calculations of correlation effects ). Unfortunately, accurate calculations as mentioned above are beyond the present computational possibilities for larger molecular structures. Therefore approximations have to be introduced in the investigation of problems of chemical interest. Consequently the reliability of calculated results has to be checked carefully for every kind of application. Three types of approximations are of interest in connection with this article. 

The interested reader is referred to two recent surveys of accurate calculations on molecules 67> and electron-pair theories 58>. A very brief introduction can also be found in Kef.18>. 

S8> Kutzelnigg, W. Electron correlation and electron pair theories. Topics Curr. Chem. 41, 31-73 (1973). 

C NMR spectra, 29 188-189 structure, 29 207-208, 218 photoelectron spectra, 29 193 polyhedral skeleton electron pair theory, 29 200... 

The geometries of metal carbonyl and metallocarborane cluster compounds have been systematized recently by a set of simple rules described collectively as the polyhedral skeletal electron pair theory (153, 218, 232). This approach originated from a perceptive analogy between isostructural metal carbonyl and borane polyhedral cluster molecules (232), and its applications have been widely discussed and reviewed (147, 153, 210, 218, 233, 234, 235, 240). In this review,... 

There is an implicit assumption contained in all of the above The two bonding electrons are of opposite spin. If two electrons are of parallel spin, no bonding occurs, but repulsion instead curve /, Fig. 5.1). This is a result of the Pauli exclusion principle. Because of the necessity for pairing in each bond formed, the valence bond theory is often referred to as the electron pair theory, and it forms a logical quantum-mechanical extension of Lewis s theory of electron pair formation. 

Polyhedral carboranes (continued) seven-vertex carboranes, 3, 58 six-vertex carboranes, 3, 56 small carborane syntheses, 3, 54 subicosahedral carborane geometrical patterns, 3, 50 subicosahedral and icosahedral, 3, 51 supraicosahedral, characteristics, 3, 96 ten-vertex carboranes, 3, 60 thirteen-vertex carboranes, 3, 100 tricarbaborane synthesis, 3, 54 twelve-vertex carboranes, 3, 98 Polyhedral skeletal electron pair theory, Ru and Os tetranuclear clusters, 6, 874-875 Poly(iV-heterocyclic carbene) ligands... 

Ru3(CO)12 with Pt(PBu )2 at room temperature affords 92 as the main product, whereas reaction in refluxing hexane affords small amounts of octanuclear cluster 93 and tetranuclear 94. The capped-pentagonal bipyr-amidal 93 contains 104 cluster electrons, or six fewer than predicted by the Polyhedral Skeletal Electron Pair Theory. Solutions of 93 slowly decompose to give a small amount of 93, together with Pt3(CO)3(PBu3)3. No platinum homologue of 91 has yet been isolated.63... 

This method, Huckel s 1st method or the H(eitler) L(ondon) S(later) P(auling) method or the Valence bond (V.B.) method, fits directly on to the electron pair theory of valency of Lewis, Langmuir, Ingold and others. Each configuration can be described by bond lines, each of which signifies an electron pair between the various atoms. It can be proved that these lines never intersect in the canonical structures configurations, in which this is the case, can be regarded as combinations of the former. 

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