Unimolecular Rearrangements, and Thermal Eliminations

Cycloaddition reactions result in the formation of a new ring from two reacting molecules. A concerted mechanism requires that a single transition state, and therefore no intermediate, lie on the reaction path between reactants and adduct. Two important 

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Concerted Cycloadditions, Unimolecular Rearrangements, and Thermal Eliminations... 

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