Bluffton University

CEM 311
Advanced Organic Chemistry

The Diels-Alder Reaction

This page is under construction.

These examples include both MO diagrams and online molecular models.

Index BACK to the CEM311 home page

Development of the Diels-Alder reaction for organic synthesis allowed the facile creation of six-membered rings and improved routes to natural products. For this, Otto Diels and Kurt Alder won the 1950 Nobel Prize in Chemistry. But explaining the reaction simply took almost twenty years, leading Roald Hoffman and R.B. Woodward on a journey through the theory of pericyclic reactions, the publication of a classic text (The Conservation of Orbital Symmetry), and a Nobel Prize for Hoffman--which Woodward would undoubtedly have shared, had he lived.

Like all pericyclic reactions, the Diels-Alder reaction can be explained in terms of the π molecular orbitals of the reactants. For the prototypical Diels-Alder reaction, between butadiene and ethylene, there are two requirements:

  1. one molecule must donate electrons, from its Highest Occupied Molecular Orbital (HOMO), to the Lowest Unoccupied Molecular Orbital (LUMO) of the other; and
  2. the two interacting orbitals must have identical symmetry--or, more simply, the phases of the terminal p-orbitals of each MO must match.
Below are shown two possible ways for this to happen: the HOMO of the diene combining with the LUMO of the dienophile, and the LUMO of the diene with the HOMO of the dienophile.

orbital overlap in the Diels-Alder reaction

Transition state for the simplest Diels-Alder reaction

BC OrgChem PageGo to the Bluffton Organic Chemistry page

Copyright © 2001 by Daniel J. Berger. This work may be copied without limit if its use is to be for non-profit educational purposes. Such copies may be by any method, present or future. The author requests only that this statement accompany all such copies. All rights to publication for profit are retained by the author.