The Diels - Alder reaction is named after Otto Diels and Kurt Alder. In 1950 they were awarded the Nobel Prize for their work on this reaction. The Diels - Alder reaction is a cycloaddtion reaction between a two conjugated double bonds (a diene) and a carbon carbon double bond or triple bond (dienophile). The reaction is very important because two new carbon-carbon bonds and a cyclohexene ring are formed in a single step. The recation mechanism is pericyclic or concerted. In other words, the reaction is a single step process with no intermediates.

Below is an interactive model of a Diels-Aldert reaction between cyclopentadiene and maleic anyhydride. By selecting the atoms which form the new ring, you can better visualize how the reaction takes place. You may also rotate the molecule to get any perspective you like.
C = grey; H = cyan; O = red

Alignment for endo transition state	Endo TS New bonds formed	Product All bond angles correct
Highlight C's	Highlight C's	Highlight C's
Highlight C's & H's	Highlight C's & H's	Highlight C's & H's
Highlight O's	Highlight O's	Highlight O's
Highlight atoms to form new ring	Highlight new ring	Highlight new ring
Reset model	Reset model	Reset model

Below are interactive models of the favored endo and unfavored exo transition states for the Diels-Aldert reaction between cyclopentadiene and maleic anyhydride. By selecting the atoms which form the new ring, you can better visualize how the reaction takes place.
C = grey; H = cyan; O = red

Alignment for endo transition state	Alignment for exo transition state

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Created March 11, 1998. KC Russell, University of Miami
Last updated March 7, 2003 Northern Kentucky University
© 1998-2003 KC Russell