Identifying a Diels-Alder Reaction

Cyclopentadiene and Nitroethylene(nitroethene)

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Diels-Alder reactions are cycloadditions which occur between a diene and a conjugated alkene, known as the dienophile.

Two sigma bonds are formed or broken in one concerted step - there are no intermediates at all. This type of reaction is known as a pericyclic reaction. As seen above, the endo transition state leads to the nitro group being opposite the CH2 bridge - for more information about endo and exo see this page.

Recognising a Diels-Alder product is easy. Look for a six memebered ring with a double bond inside the ring and a conjugating group outside the ring on the opposite side to the double bond.

Other pages of interest to do with Animated Molecular Orbitals are

Introductory | Pericyclic Reactions and Heck Catalytic Cycle