The Diels-Alder reaction of cyclopentadiene ("diene" component) and acetylene derivatives ("dienophile") yields a single product. The animations visualize the relative arrangements of the diene and dienophile with different view points.

The Diels-Alder reaction of cyclopentadiene ("diene" component) and maleic acid anhydride ("dienophile") yields both the endo- and exo-products, the former being the kinetically controlled product while the latter is thermodynamically favored (more stable). The reversible reaction proceed as a concerted [4p_s + 2p_s] cycloaddition in which both carbon-carbon bonds are formed or broken simultaneously. The animations visualize the relative arrangements of the diene and dienophile which determine whether the endo- or exo-product is being formed.

Diels-Alder reaction of the different 2,4-hexadienes (trans,trans-, cis,trans-, trans,cis-, or cis,cis-) with acroleine as the dienophile result in racemic endo- or exo-products with respect to the position of the CHO-group. The [4p_s + 2p_s] cycloaddition is highly stereospecific and the geometry of the diene is fully retained in the cyclohexene type products. Vice versa, the relative configuration of the cyclohexene determines the configuration of the resulting diene in the reverse reaction (disrotatory motion). The course of the Diels-Alder reaction is determined by the relative symmetry of the HOMO of the diene (cyclopentadiene) and the LUMO of the dienophile (acroleine). The animations show the stereospecificity of the cycloaddition between all four isomeric 2,4-hexadienes and acroleine.

Please note the increasing distortion due to steric crowdance and non-planar conformation of the diene in the order trans,trans < cis,trans = trans,cis << cis,cis. At least for the latter cis,cis-2,4-hexadiene the Diels-Alder reaction is not a favored process.