Woodward–Hoffmann rules

set of rules used to rationalize or predict certain aspects of the stereochemistry and activation energy of pericyclic reactions

The Woodward–Hoffmann rules are a set of organic chemistry rules to predict the stereochemistry of pericyclic reactions. Pericyclic reactions are usually rearrangement reactions where the molecule is a ring (e.g. benzene ring).[1] They were written by Robert Burns Woodward (a chemistry professor at Harvard University) and Roald Hoffmann (a chemistry professor at Cornell University). Hoffmann was awarded the 1981 Nobel Prize in Chemistry for this work, shared with Kenichi Fukui who developed a similar model.[2] Woodward did not share the prize because he died two years before. Generally, the Nobel Prize is awarded only to living people. Woodward had already won a Nobel Prize in Chemistry for a different discovery.

Robert Burns Woodward
Roald Hoffmann

A recent paper in the journal Nature describes how mechanical stress can be used to reshape chemical reaction pathways to lead to products that apparently violate Woodward–Hoffman rules.[3]

Related pagesEdit


  1. The rules are based on molecular orbital symmetry. The rules cover electrocyclic reactions, cycloadditions (including cheletropic reactions), sigmatropic reactions, and group transfer reactions.
  2. "The Nobel Prize in Chemistry 1981". Nobel Media AB. Retrieved 2011-07-22.
  3. Biasing reaction pathways with mechanical force. Nature 2007 446:423-427 (See also the corresponding "News and Views" in the same issue of Nature)

Other websitesEdit

  • Symmetry rules!, Sophie Wilkinson Chemical & Engineering News January 27, 2003 Volume 81, Number 04 CENEAR 81 04 pp. 59 ISSN 0009-2347 Article
  • "SHMO calculator", Simple Huckel molecular orbital theory calculator Link Archived 2009-11-22 at the Wayback Machine