Extended Hiickel molecular orbital

YAcHMOP stands for yet another extended Hiickel molecular orbital package. The package has two main executables and a number of associated utilities. The bind program does molecular and crystal band structure extended Hiickel calculations. The viewkel program is used for displaying results. We tested Version 3.0 of bind and Version 2.0 of viewkel. 

Extended Hiickel molecular-orbital (EHMO) calculations using structural parameters from the X-ray determination of Cp(CO)3Mo 3In (Fig. 29) and ideal symmetry Cih were carried out for this compound in order to investigate the extent of the indium-molybdenum ir-bonding.122 The HOMO of the compound is the 3e molecular orbital, which is In—Mo [Pg.54]

The Dotz reaction mechanism has received further support from kinetic and theoretical studies. An early kinetic investigation [37] and the observation that the reaction of the metal carbene with the alkyne is supressed in the presence of external carbon monoxide [38] indicated that the rate-determining step is a reversible decarbonylation of the original carbene complex. Additional evidence for the Dotz mechanistic hyphotesis has been provided by extended Hiickel molecular orbital [23, 24] and quantum chemical calculations [25],... 

Were the isoelectronic anion (i.e., C2B3Hg ) to be prepared, the most stable configuration should have adjacent basal carbons to accommodate the basal bridge hydrogen as well as the carbon. Either cis or trans basal carbons should be anticipated in the isoelectronic dianion (C2B3H5 ) which would have no bridge hydrogens. Rudolphs s Extended Hiickel Molecular Orbital calculations would favor cis basal carbons in the latter case. 

From iterative extended Hiickel molecular orbital (EHMO) calculations, [VX]"+ (X = S, Se n = 0, 1, 2) ions and their tetrachloro complexes [VXCl4]m- (m = 4, 3, 2) decrease in stability 0>S>Se and with increasing charge of the anion.695 The [VXC14]2- and [VXCI4]4-complexes are expected to be S = systems while [VXC14]3- species are expected to be diamagnetic.695... 

Extended Hiickel molecular orbital calculations have been made for the icosahedral platinaboranes and carbaboranes [Bn Pt(PH3)2 Hu]2-, [Bi0C Pt(PH3)2 Hu]2, and... 

It has been found that whereas Cu11 porphyrins luminesce, the Ag" complexes do not. By an examination of electronic absorption spectra, emission spectra, redox potentials and near-IR absorption data, it was proposed that this could be rationalized on the basis of the energy of the big (dx2 yi) orbital. Extended Hiickel molecular orbital calculations predicted that the d-n transition would be above the lowest (n, jt ) levels for Cu11 but below them in the Agn complexes. The near-IR absorptions found for Ag11 were attributed to CT transitions.554... 

Studies of the tautomeric state of 1,2,4-thiadiazines have been more or less confined to the biologically active 1,2,4-benzothiadiazines. Ultraviolet spectroscopic studies suggest that the 4//-tautomer of 1,2,4-benzothiadiazines, e.g. 152, is preferred in ethanol (60JOC970) in alkali, the anion dominates. Extended Hiickel molecular orbital calculations (70MI2) and 13C-NMR studies (79T2151) confirm this view (Scheme 6). 

Hiickel molecular orbitals in porphin were investigated by Longuet-Higgins et al. (68), and the extended Hiickel molecular orbital model was applied to metalloporphyrins in attempts by Pullman et al. (93), Ohno et al. (86), and Zerner et al. (120) to explain various experimental observations. Let us briefly consider a description of cyanoferriporphin. According to the Hiickel theory all but the -orbitals of each carbon and nitrogen atom of porphin are used up to form the relatively inert skeleton of single bonds. To describe the -bonding twenty-four molecular orbitals of porphin can then be formed as linear combinations of... 

Chapter 1 of Volume 15 deals with density functional theory (DFT). As with many quantum mechanical calculations, it is easy to become wrapped up in the theory and lose sight of the chemical phenomena we are trying to explain with the calculations. Equally important to how the numerical calculations are done is how the results can be interpreted to gain chemical insight. Dr. F. Matthias Bickelhaupt and Professor Evert Jan Baerends show how the results of DFT calculations can be analyzed to open up chemical understanding. This chapter illustrates that the plain numbers from a quantum mechanical calculation can be interpreted to be conceptually useful to chemists. In many ways, this chapter evokes memories of the famous way Professor Roald Hoffmann has extracted information from extended Hiickel molecular orbital calculations. 

Silvestre and Hoffmann have considered the conversion of ruthenium acetylide complexes to the corresponding vinylidene species using extended Hiickel molecular orbital calculations (69). Although the rearrangement of free acetylene to its vinylidene isomer is thermodynamically disfavored, their results indicate that the transformation becomes thermodynamically... 

This is, in principle, in agreement with extended Hiickel molecular-orbital calculations. The calculated binding energy and difference between the energies of the LUMO and HOMO for the four possible isomers indicate the experimentally isolated structure to be the most stable one, although the extended Hiickel calculation does not show a substantial relative stability (Table I). 

An extended Hiickel molecular orbital analysis on both of these complexes revealed that this structural difference between the chloride and the iodide can be traced to a second-order Jahn-Teller distortion, which is predicted to occur more readily for the chloride. Specifically,... 

If the above generalization is correct, then simple extended Hiickel molecular orbital calculations for the surface chemisorption states of simple hydrocarbons or hydrocarbon fragments should sense this tendency for multicenter C-H-metal bonds to form (these... 

Concerted two-electron transfer and reversible metal-metal bond cleavage in phosphine-bridged dimers have been investigated, and extended Hiickel molecular orbital calculations have shown that the redox-active orbital is a metal-metal antibonding orbital. A Ru-Ru-bonded dimeric cation [Ru(Cp)2]2++ has been prepared and characterized electrochemically. The electrochemistry of these dimers may give insight into more complex clusters and polymeric metals. 

The band structure of a three-dimensional solid, such as a semiconductor crystal, can be obtained in a similar fashion to that of a polyene. Localized molecular orbitals are constructed based on an appropriate set of valence atomic orbitals, and the effects of delocalization are then incorporated into the molecnlar orbital as the number of repeat units in the crystal lattice is increased to infinity. This process is widely known to the chemical conununity as extended Hiickel theory (see Extended Hiickel Molecular Orbital Theory). It is also called tight binding theory by physicists who apply these methods to calcnlate the band structures of semiconducting and metallic solids. 

Whereas empirical force-field calculations predict a ring A boat conformation for lanost-8-en-3-one, combined empirical force-field-extended Hiickel molecular orbital calculations favour a ring A chair conformation. Europium-shift n.m.r. results indicate that the molecule adopts the latter conformation. Studies on the peracetic acid-boron trifluoride etherate Baeyer-Villiger oxidation of 4,4-dimethyl-3-keto-triterpenoids to 5-lactones (18) and their subsequent ring contraction to y-lactones have been reported. Dehydrogenation of lanost-8-en-3j8-ol with 2,3-dichloro-5,6-dicyanobenzoquinone afforded, in addition to the corresponding 7,9(1 l)-diene, the aromatic seco-lanostane derivatives (19)... 

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