Chelotropic reaction

The book is divided into three parts. Part I deals with typical complex organic reactions such as (i) reactions involving carbocations and carbanions, (i/) Pericyclic and electrocyclic reactions and (ii/) Sigmatropic and Chelotropic reactions. This part also includes material useful for characterization of products from structural point of view such as Geometrical isomerism, Stereochemistry and Conformation. Part II is concerned with spectroscopic methods of structure determination such as U.V.,... 

Ab initio calculations at the MP2(FC)/6-31G //RHF/6-31G level show that the chelotropic reactions of 1,3-dienes with SO2 cannot he two-step as recently reported. 

How new are these three computer predicted organic reactions One could raise the objection, that there are similar known organic reactions (the last example is a chelotropic reaction). The answer is easy to give within our hierachical model of reaction classification. We can define a degree of novelty or innovation of chemical reactions ... 

Definitions of linear and nonlinear approaches in chelotropic reactions. 

Theoretical approaches to chelotropic reactions, showing only allowed reaction paths. A. An FMO analysis. B. Hiickel vs. Mobius transition states. C. Use of the generalized orbital symmetry rule. 

The term chelotropic reaction refers to reactions in which an odd-numbered ring is formed by addition of a monocentric reagent across the end of an even, conjugated system. The classic example is the formation of the sulfone (214) by addition of sulfur dioxide to butadiene,... 

In a chelotropic reaction, the reagent has to have two AOs available to form the new bonds. These AOs must also contain just two electrons between them in order that the new bonds be covalent rather than dative. Thus we can write SO2 in the form (215) with a filled hybrid AO (i) and an empty 3p AO (2). 

FIGURE 5.38. (a) Interaction of hybrid AOs of (216) to form the correct AOs of (215), p being the resonance integral between the hybrid AOs (b) analogous interaction between 2p AOs of the two carbon atoms in ethylene to form bonding n ) and antibonding (n ) MOs (c) transition state for the Diels-Alder reaction between butadiene and ethylene (cf. Fig. 5.35) (d) transition state for the chelotropic reaction of equation (5.317). 

FIGURE 5.39. Disroiatory chelotropic reaction of SO2 with a 4it-poLyene. 

FIGURE 5.40. Conrotatory chelotropic reaction of SO2 with a (4n + 2)-polyene. The orbitals of SO2 are the two hybrid AOs of (216), the dotted line indicating the interaction between them. 

The first step is a disrotatory chelotropic reaction, the transition state being isoconjugate with naphthalene (218). The second step is a conrotatory electrocyclization, the transition state being isoconjugate with an anti-Hiickel analog of (219). 

The addition of carbene to an olefin could be regarded as the simplest possible chelotropic reaction and indeed Woodward and Hoffmann class it as such e.g.,... 

Quantitative M.O. models were used in a discussion of the photoelectron spectrum of thiiran 1,1-dioxide. As compared with dimethyl sulphone, all antibonding S—C cr-orbitals increase in energy and bonding S—C a-orbitals decrease in energy because of the relative compression of the S—C bonds in the cyclic sulphone. The chelotropic reactions of thiiran 1,1-dioxide have been compared with the formation of alkene-oxygen Tr-complexes. Activation parameters for the extrusion of sulphur dioxide from thiiran 1,1-dioxide have been obtained. ... 

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