Maximum symmetry analysis

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

This can be realized either in a planar structure or, if steric interactions prevail, in a twisted conformation where the X—C—X plane makes an angle of any value, except 90 °, with the C=C—H plane. The 90 °C twisted form where the X group is en-antiomerically related is probably the conformation of maximum energy required for the interchange of the two X groups. Similar symmetry analysis can be invoked to describe the conformations associated with the two interchanging R groups, as has been observed in the NMR. 

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>. 

A guiding principle in the following analysis is the principle of maximum symmetry which states that ... 

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... 

Theoretical Aspects, Calculations, and Physical Data.—The basis of orbital-corre-pondence analysis in maximum symmetry has been described in terms of the familiar A and S notation, and the relationship to the Woodward-Hoffmann and Longuet-Higgins-Abrahamson analyses of pericyclic reactions discussed. In a useful and... 

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. 

In the early discussions of hybrid orbitals4,5 it was pointed out that the maximum strength (the maximum value in the bond direction) of a bond orbital formed from completed subshells of orbitals is associated with cylindrical symmetry of the orbital. In order to simplify the analysis of spd hybridization Hultgren5 decided to discuss only orbitals with cylindrical symmetry. He pointed out that no more than three d orbitals with cylindrical symmetry can be formed in a set of five d orbitals, and that each of these three is equivalent to the function d2 (see Table 1), except in orientation. 

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