Htickel Molecular Orbital Theory

For excellent discussions of this method see Woodward, R.B. Hoffmann, R. Ref. 1256 Jones, R.A.Y. Physical and Mechanistic Organic Chemistry, 2nd ed. Cambridge University Press Cambridge, 1984, p. 352 Klumpp, G.W. Reactivity in Organic Chemistry, Wiley NY, 1982, p. 378 Yates, K. Htickel Molecular Orbital Theory, Academic Press NY, 1978, p. 263. 

Use of Htickel Molecular Orbital Theory in Interpreting the Visible Spectra of Polymethine Dyes 172... 

McClelland, B.J. (1974). Graphical Method for Factorizing Secular Determinants of Htickel Molecular Orbital Theory. J.Chem.Soc. Faraday Trans II, 70,1453-1456. 

Benzene is described by molecular orbital theory as a planar, cyclic, conjugated molecule with six it electrons. According to the Htickel rule, a molecule must have 4n + 2 77 electrons, where n - 0, 1, 2, 3, and so on, to be aromatic. Pianar, cyclic, conjugated molecules with other numbers of tt electrons are antiaromatic. 

In Chapter 5, conventional simple Htickel molecular orbital (SHMO) theory is introduced. The Htickel a is suggested as a reference energy, and use of / as a unit of energy is advocated. Parameters for heteroatoms and hybridized orbitals are given. An interactive computer program, SHMO, which uses the conventions introduced in this chapter, is available on the Web [12]. 

HUckel (p. 328) was a pioneer in the field of molecular orbital theory. He developed the LCAO method in its simplest form, yet Htickel molecular orbitals have proved enormously successful in dealing with organic molecules. Htickel proposed the 4/i + 2 rule in 1931. It has been tested in many ways since then, and it works. Now, what is the theoretical basis for this rule ... 

Erich Htickel was a German physical chemist first known for his collaboration with Peter Debye in developing what remains the most widely accepted theory of electrolyte solutions, then later for his application of molecular orbital theory to conjugated hydrocarbons, especially aromatic hydrocarbons (Chapter 11). 

W. Htickel, also provided a basis for a rational description of molecular orbitals in these systems. An extended Htickel theory allowed a study of molecular orbitals throughout chemistry at a certain level of approximation. 

A formalized analysis of the EFG was also employed by Bagin et al. (1980) their model effectively explained the large quadrupole splitting that is associated with octahedral Fe, again using vacancies as part of their model. More recently, an elegant paper by Aldridge et al. (1986) used molecular orbital methods to model the electronic structure of biotite. They showed that iterative extended Htickel theory calculations of... 

The most accurate computations of the intermolecular coupling are carried out at the DFT level of theory (usually involving hybrid functionals such as B3LYP) with the molecular orbital expanded in a medium to large atomic basis set. Less accurate but very fast computations are done using the semiempirical ZINDO Hamiltonian which has been optimized for electronic spectroscopy and has been validated against DFT a number of times [92]. More elementary extended Htickel computations were... 

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