Orbital correspondence analysis

Just for the sake of completeness it is worthwhile mentioning that, according to the orbital correspondence analysis, this W2S + n2a cycloaddition of ethylene is also thermally forbidden [71], Quantum chemical calculations [72] reported a transition structure for this thermally allowed concerted reaction, but due to steric repulsions between some of the hydrogens, this transition structure is very high in energy. Indeed, the reaction is not observed experimentally. 

E. A. Halevi, Orbital Correspondence Analysis in Maximum Symmetry. Helv. Chim. Acta 1975, 58, 2136-2151. 

An analysis of the dimerization of silacyclopropene was carried out by Orbital Correspondence Analysis in Maximum Symmetry (OCAMS). This analysis showed that the dimerization of silacyclopropene follows an allowed pathway <82JOM(240)129>. 

Huisgen s mechanism was also discussed on the basis of the principle of orbital correspondence analysis in maximum symmetry (OCAMS) by Halevi (1992, p. 168). 

OCAMS orbital correspondence analysis in maximum symmetry... 

In their now classic monograph [1], Wooodward and Hoffmann concentrate on three basic types of no mechanism reaction Electrocyclic reactions -notably polyene cyclizations, cycloadditions, and sigmatropic rearrangements. These three reaction types will be taken up in this and the next two chapters from the viewpoint of Orbital Correspondence Analysis in Maximum Symmetry (OCAMS) [2, 3, 4], the formalism of which follows naturally from that developed in Chapter 4. The similarities to the original WH-LHA approach [5, 6], and the points at which OCAMS departs from it, will be illustrated. In addition, a few related concepts, such as allowedness and forbiddenness , global vs. local symmetry, and concertedness and synchronicity , will be taken up where appropriate. 

Professor Halevi has set out to correct the situation by making available a rigorously written text. He relies on a particularly well thought-through formulation, referred to as Orbital Correspondence Analysis in Maximum Symmetry (OCAMS). The playful reference to the medieval scholar, Occam, whose fabled razor all students are told about, is well chosen this is a text of high intellectual and scholarly standards. 

My object in writing this book is to present a coherent set of operational rules for the analysis of reaction mechanism in terms of symmetry, and to explore their scope and reliability. It is written from the viewpoint of Orbital Correspondence Analysis in Maximum Symmetry - OCAMS for short, hence its subtitle, but not with the intention of touting a homemade prodct The procedural details of OCAMS are of secondary importance its advantage lies in the provision of a coherent overview of the relation between symmetry and mechanism it allows us to see the forest without losing sight of the trees. For reasons of self-consistency, the book remains within the framework of molecular orbital theory reformulation of the OCAMS approach in valence-bond terms has not been attempted. 

The prediction on the basis of orbital symmetry analysis that cyclization of eight-n-electron systems will be connotatoiy has been confirmed by study of isomeric 2,4,6,8-decatetraenes. Electrocyclic reaction occurs near room temperature and establishes an equilibrium that favors the cyclooctatriene product. At slightly more elevated temperatures, the hexatriene system undergoes a subsequent disrotatory cyclization, establishing equilibrium with the corresponding bicyclo[4.2.0]octa-2,4-diene ... 

For large molecules, the equivalent-orbital analysis is the most convenient starting point for a molecular-orbital treatment. In a molecule such as a long-chain paraffin it is possible to write approximate equivalent orbitals corresponding to each bond and then to apply a transformation to obtain the delocalised molecular orbitals. Simple assumption about, the interaction of neighbouring bonds will then lead to estimates of the relative stability of the various energy levels.9... 

Further analysis allows us to single out two types of contributions to the parameter Hm- It can be broken down into a sum of a component which is, however, dependent on the hybridization of the entering orbitals corresponding to the bond itself and the rest describing the environment of the bond ... 

Orbital symmetry analysis of the 1,5-sigmatropic shift of hydrogen leads to the opposite conclusion. The relevant frontier orbitals in this case are the hydrogen Is and 1/ 3 of the pentadienyl radical. The suprafacial mode is allowed, whereas the antarafacial mode is forbidden. The suprafacial shift corresponds to a geometrically favorable six-membered ring. 

The electronics behind olefin coordination to group 4 cationic L2MtR+ species has been studied in details by Marynick, Morokuma, and co-workers. ° Their analysis indicates that while the Mt—R bond in the Cs-symmetric Cl2TiCH3+ species chiefly involves a metal orbital which corresponds to the lai orbital of Figure 1, the olefin coordination is due to in-phase interactions between the olefin r-orbital with metal orbitals corresponding to the 2ai, mainly, and to one lobe of the lb2 orbitals of Figure 1. A good overlap between the olefin r-orbital and these metal orbitals... 

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