Pericyclic molecular electrocyclic

In this primer, Ian Fleming leads you in a more or less continuous narrative from the simple characteristics of pericyclic reactions to a reasonably full appreciation of their stereochemical idiosyncrasies. He introduces pericyclic reactions and divides them into their four classes in Chapter 1. In Chapter 2 he covers the main features of the most important class, cycloadditions—their scope, reactivity, and stereochemistry. In the heart of the book, in Chapter 3, he explains these features, using molecular orbital theory, but without the mathematics. He also introduces there the two Woodward-Hoffmann rules that will enable you to predict the stereochemical outcome for any pericyclic reaction, one rule for thermal reactions and its opposite for photochemical reactions. The remaining chapters use this theoretical framework to show how the rules work with the other three classes—electrocyclic reactions, sigmatropic rearrangements and group transfer reactions. By the end of the book, you will be able to recognize any pericyclic reaction, and predict with confidence whether it is allowed and with what stereochemistry. 

Whether they go in the direction of ring opening or ring closure, electrocyclic reactions are subject to the same rules as all other pericyclic reactions—you saw the same principle at work in Chapter 35 where we applied the Woodward-Hoffmann rules both to cycloadditions and to reverse cycloadditions. With most of the pericyclic reactions you have seen so far, we have given you the choice of using either HOMO-LUMO reasoning or the Woodward-Hoffmann rules. With electrocyclic reactions, you really have to use the Woodward-Hoffmann rules because (at least for the ring closures) there is only one molecular orbital involved. 

M. J. S. Dewar, A Molecular Orbital Theory of Organic Chemistry-VIII Aromaticity and Electrocyclic Reactions. Tetrahedron Suppl. 1966,8,75-92 Aromaticity and Pericyclic Reactions. Angew. Chem. Int. Ed. Engl. 1971, 10,761-776 The Molecular Orbital Theory of Organic Chemistry, McGraw-Hill, New York, 1969. 

In analyzing pericyclic reactions, two molecular orbitals are of particular interest the tt molecular orbital of highest energy that contains one or two electrons (the highest occupied molecular orbital, HOMO) and the molecular orbital of lowest energy that contains no electrons (the lowest unoccupied molecular orbital, LUMO). For electrocyclic reactions, where there is only one TT system, the important orbital is the HOMO. When more than one tt system is involved, as in (ycloaddition, reactions are considered to occur through a transition state in which the HOMO of one component overlaps the LUMO of the other. 

Abstract A discussion on conservation of orbital symmetry and its application to select pericyclic reactions is presented. Initially, effort is made to explore the symmetry characteristics of the cr, cr, n and n molecular orbitals (MOs). This is followed by a description of the MOs and their symmetry characteristics for allyl cation, allyl radical, allyl anion, and 1,3-butadiene. This concept is applied to n2 + n2, n4 + it2 (Diels-Alder) and electrocyclic reactions. 

Discuss Frontier Molecular Orbital (F.M.O.) method for pericyclic reactions. What are electrocyclic reactions Drawing correlation diagram, describe the comrotatoiy and disrotatory interconversion of cyclobutene and butadiene. Discuss Frontier Molecular Orbital (F.M.O.) method of analysing electrocyclic reactions. Derive selection rules for electrocyclic reactions. What are electrocyclic reactions Drawing correlation diagram discuss disrotatory and conrotatory interconversion of cyclobutene and butadiene. Support the results of correlation diagram by F.M.O. theory. 

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