Electronic configuration molecular orbitals

It is the unique ability of the strained epoxy ring to react with a wide variety of reactants under many diverse conditions that gives epoxies their versatility (95). Detailed discussions on the probable electronic configurations, molecular orbitals, bond angles, and reactivity of the epoxy ring are available in the literature (96). 

The oxygen molecule is paramagnetic with a moment in accord with two unpaired electrons. In molecular orbital terms, the configuration is written... 

The CH3XY complex with 21 valence electrons is formally equivalent to the trihalogen YXY (or ZXY) complex which also has 21 valence electrons, while the HXY complex has 15 valence electrons. The molecular orbital configurations are... 

Figure 1. The electron configurations for four electrons using molecular orbitals obtained as linear combinations of atomic orbitals.

The reactivity of the excited species will be influenced by both its energy level and rearranged electron configuration. Excited species are usually both better electron donors and electron acceptors than their parent molecules. The excited electron would be more readily donated while the low-energy vacancy left by the excited electron would more readily accept an electron. The redistribution of electrons in molecular orbitals may influence shape and dipole moments. Hydrogen abstraction is a common reaction of excited species. For example, benzophenone in the presence of a suitable donor solvent such as ethanol is readily reduced to the alcohol. 

For homonuclear diatomic molecules, a g or m right subscript is added to the term symbol to show the parity of the electronic states belonging to the term. Terms arising from an electron configuration that has an odd number of electrons in molecular orbitals of odd parity are odd (u) all other terms are even (g). This is the same rule as for atoms. 

It was decided to improve these calculations by using better electronic wavefunctions 0. Single configuration molecular orbital wavefunctions were still used. However, the molecular orbitals were expressed in terms of a so-called extended basis set of gaussian atomic orbitals (for details see reference (3)). The Hartree-Fock-self-consistent-field (HFSCF) procedure was carried out with the digital computer program POLYATOM, The quality of the wavefunctions is not quite what would be called Hartree-Fock limit wavefunctions. Calculations were carried out at several intemuclear distances and C was calculated with the inclusion of the factor A correctly calculated. The calculations were extended to include the ground states of several ions and also of HCl. 

Late Dr. Isaiah Shavitt has been the champion of configuration-interaction (Cl) theory [1-4], which is the first systematically accurate, ab initio electron-correlated molecular orbital (MO) theory. Although today its usage may be diminished with the advent of coupled-cluster (CC) theory [5], its predictions have overturned some experimental conclusions [6, 7] and helped computational quantum chemistry be accepted by a broader community of chemists as a vital engine of chemical research. 

Electrons in Molecular Orbitals Several aspects of MO theory—filling of MOs, energy-level diagrams, electron configuration, and bond order—relate to earUer ideas ... 

Molecules. The electronic configurations of molecules can be built up by direct addition of atomic orbitals (LCAO method) or by considering molecular orbitals which occupy all of the space around the atoms of the molecule (molecular orbital method). 

In practice, each CSF is a Slater determinant of molecular orbitals, which are divided into three types inactive (doubly occupied), virtual (unoccupied), and active (variable occupancy). The active orbitals are used to build up the various CSFs, and so introduce flexibility into the wave function by including configurations that can describe different situations. Approximate electronic-state wave functions are then provided by the eigenfunctions of the electronic Flamiltonian in the CSF basis. This contrasts to standard FIF theory in which only a single determinant is used, without active orbitals. The use of CSFs, gives the MCSCF wave function a structure that can be interpreted using chemical pictures of electronic configurations [229]. An interpretation in terms of valence bond sti uctures has also been developed, which is very useful for description of a chemical process (see the appendix in [230] and references cited therein). 

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