Semi-empirical molecular orbital theory

While physical modeling has been important historically, and is still a central part of chemical education and some investigations in stereochemistry, contemporary chemical models are almost always mathematical. Families of partially overlap>-ping, partially incompatible models such as the valence bond, molecular orbital, and semi-empirical models are used to explain and predict molecular structure and reactivity. Molecular mechanical models are used to explain some aspects of reaction kinetics and transport processes. And lattice models are use to explain thermodynamic properties such as phase. These and other mathematical models are ubiquitous in chemistry textbooks and articles, and chemists see them as central to chemical theory. 

Thiel W 1996 Perspectives on semiempirical molecular orbital theory New Methods in Computationai Quantum Meohanios (Adv. Chem. Phys. XCiti) ed I Prigogine I and S A Rice (New York Wiley) pp 703-57 Earlier texts dealing with semi-empirical methods include ... 

Presell is the basic theory of tjuaiiHim mechanics, particularly, semi-empirical molecular orbital theory. The authors detail and justify the approximations inherent in the semi-empirical Ham illoTi ian s. Includes useful discussion s of th e appiicaliori s of these methods to specific research problems. 

In this section, the conceptual framework of molecular orbital theory is developed. Applications are presented and problems are given and solved within qualitative and semi-empirical models of electronic structure. Ab Initio approaches to these same matters, whose solutions require the use of digital computers, are treated later in Section 6. Semi-empirical methods, most of which also require access to a computer, are treated in this section and in Appendix F. 

J. N. Murrell, A. J. Harget, Semi-empirical self-consistent-field molecular orbital theory of molecules John Wiley Sons, New York (1972). 

Provides a survey of quantum mechanics, semi-empirical computational methods, and the application of molecular orbital theory to organic chemistry. The concepts explored in this book should be easy for most readers to understand. 

Murrell, J. N. Harget, A. J. Semi-empirical Self-consistent-field Molecular Orbital Theory of Mo/ecw/e Wiley Interscience, New York, 1971. 

J. N. Murrell and A. J. Harget, Semi-empirical Self-consistent Molecular Orbital Theory of Molecules, Wiley-Interscience, London, 1972 G. H. Wagniere, Introduction to Elementary Molecular Orbital Theory and to Semiempirical Methods, Springer-Verlag, Berlin, 1976 J. Sadleij, Semi-empirical Methods of Quantum Chemistry, Wiley, New York, 1985. 

Molecular orbital theory is a semi-empirical method devoted to interpreting the energy-level structure of optical centers where the valence electron cannot be considered as belonging to a specific ion. In our ABe reference center, this would mean that the valence electrons are shared by A and B ions. The approach is based on the calculation of molecular orbitals (MO) of the ABe pseudo-molecule, V mo, from various trial combinations of the individual atomic orbitals, V a and of the A and B ions, respectively. The molecular orbitals V mo of the center ABe are conveniently written in the form... 

Fenske, R. F. Semi-empirical molecular-orbital theory for transition-metal complexes. Inorg. Chem. 4, 33 (1965). 

As presented, semi-empirical methods are based on a single-configuration picture of electronic structure. Extensions of such approaches to permit consideration of more than a single important configuration have been made (for excellent overviews, see Approximate Molecular Orbital Theory by J. A. Pople and D. L. Beveridge, McGraw-Hill, New York... 

The drug designer must consider the susceptibility to, and consequences of, the principal Phase 1 metabolic reactions hydrolysis, reduction and oxidation. Susceptibility to oxidation can be calculated using semi-empirical molecular orbital theory. Ease of oxidation is reflected by the energy of the HOMO, and the probable site of oxidation can be predicted from calculation of the electrophilic superdelocalizability. Likewise, ease of reduction is related to LUMO energy, and probable site to nucleophilic superdelocalizability (Loew and Burt, 1990). 

J. N. Murrell and A. J. Haiget, Semi-empirical Sef-consistent-Field Molecular Orbital Theory of Molecules, Wiley-Interscience, London, England, 1972. 

Hiickel and extended Huckel methods are termed semi-empirical because they rely on experimental data for the quantification of parameters. There are other semi-empirical methods, such as CNDO, MINDO, INDO, in which experimental data are still used, but more care is taken in evaluating the Htj. These methods are self-consistent field procedures based on 3 SCF. They are discussed in various works on molecular orbital theory.4... 

The contributions of Erich Hiickel to the development of molecular orbital theory have already been mentioned in the subsection on Germany (Section 5.4.1) the development of semi-empirical quantum mechanical treatments in organic chemistry by M. J. S. Dewar has been discussed in Section 5.5. In the early development of the application of quantum mechanics to chemistry, Linus Pauling (1901-1994)359 was pre-eminent. He was associated with CalTech for most of his career. His work before World War II generated two influential books the Introduction to Quantum Mechanics (with E. Bright Wilson, 1935)360 and The Nature of the Chemical Bond (1939).361 He favoured the valence-bond treatment and the theory of resonance. 

The most satisfactory treatments of hydrogen bonding use either ab initio or semi-empirical molecular orbital theory. The most stable form of the dimer has the configuration shown in Fig. 1 (Shipman et al., 1974 Stillinger and Lemberg, 1975), It is generally assumed, in the absence of information to the contrary, that in water, ice and hydrates one H-atom is collinear with the two oxygen atoms. 

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