Molecular orbital theory general principles

MO (molecular orbital) theory (Appendix 5). Our experience has been (and continues to be) that although this approach is important to chemical bonding, most general chemistry students do not understand it but only memorize the principles discussed in the classroom. 

Dewar, M. J. S. A Molecular Orbital Theory of Organic Chemistry, I. General Principles. J. Amer. chem. Soc. 74, 3341 (1952). 

Stereochemistry is not discussed in great detail, except in the context of the Woodward-Hoffmann rules. Molecular orbital theory is also given generally short shrift, again except in the context of the Woodward-Hoffmann rules. I have found that students must master the basic principles of drawing mechanisms before additional considerations such as stereochemistry and MO theory are loaded onto the edifice. Individual instructors might wish to put more emphasis on stere-oelectronic effects and the like as their tastes and their students abilities dictate. 

The more recent treatment of the covalent bond, based on the application of the principles of wave mechanics, has developed in two distinct forms, usually termed the valence-bond and molecular-orbital theories, respectively. Although ultimately there is no inconsistency between these two theories, they do in fact approach the problem of chemical binding from different points of view, and we shall generally find that for our purposes the valence-bond treatment is the more suitable. This theory starts from concepts already familiar to the chemist and its conclusions can usually be expressed verbally in qualitative terms the molecular-orbital theory, on the other hand, is more mathematical in its approach and lends itself less readily to such an interpretation. We shall, therefore, first discuss the valency-bond theory, and refer only briefly to the molecular-orbital treatment later in the chapter. 

Chemistry. 1. General Principles ibid., 3345. A Molecular Orbital Theory of Organic Chemistry. 

This quantity can be viewed as a generalization of Fukui s frontier molecular orbital (MO) concept [25] and plays a key role in linking Frontier MO theory and the HSAB principle. It can be interpreted either as the sensitivity of a system s chemical potential to an external perturbation at a particular point r, or as the change of the electron density p(r) at each point r when the total number of electrons is changed. The former definition has recently been implemented to evaluate this function [26,27] but the derivative of the density with respect to the number of electrons remains by far the most widely used definition. 

Hybridization means the mixing of atom orbitals of different types of the given atom in one molecular (or atom) orbital. Hybridization principles are well-developed in accordance with the experimental data in the frames of general theories of valence bond (VB) and molecular orbitals (MO). 

It is well appreciated that thermodynamic and kinetic parameters are difficult to compute for organometallic molecular systems (see, e.g.. Refs 12-14 and Chap. 4 by Frenking in the present volume). In particular, such quantities cannot be predicted within an independent-particle, single-determinant Hartree-Fock type of approach electron correlation must be included in the computational methods applied to achieve reliable and accurate results. In this work, we examine the performance of three first-principles methods, generally acknowledged by the abbreviations BLYP, B3LYP, and MP2. The first two are methods based on density functional theory (DFT) (15) the latter is an ab initio, molecular orbital (MO)-based method (16). 

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