Woodward–Hoffmann rules facts for kids
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). 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. 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.
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.
Related pages
- Woodward's rules for calculating UV absorptions
- Torquoselectivity
- 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
Images for kids
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Some thermal and photochemical interconversions of substituted cyclobutenes and butadienes showing conrotatory (blue) and disrotatory (red) behavior.
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The transition state of a conrotatory closure has C2 symmetry, whereas the transition state of a disrotatory opening has mirror symmetry.
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4 electron electrocyclization reaction correlation diagram with a conrotatory mechanism.
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4 electron electrocyclization reaction correlation diagram with a disrotatory mechanism.
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First excited state (ES-1) of butadiene.
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A second excited state (ES-2) of butadiene.
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4 electron electrocyclization state correlation diagram with a conrotatory mechanism.
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4 electron electrocyclization state correlation diagram under disrotatory mechanism.
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The [2s + 2s] cycloaddition retains stereochemistry.
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The mirror plane is the only conserved symmetry element of the Diels-Alder [4+2]-cycloaddition.
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Transfer of a pair of hydrogen atoms from ethane to perdeuterioethylene.
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Conserved mirror plane in transfer reaction.
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A 4n electron electrocyclic reaction achieves constructive HOMO orbital overlap if it is conrotatory, while a 4n+2 electrocyclic reaction achieves constructive overlap if it is disrotatory.
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In [1,j]-sigmatropic rearrangements if 1+j = 4n, then supra/antara is thermally allowed, and if 1+j = 4n+2, then supra/supra or antara/antara is thermally allowed.
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The [3,3]-sigmatropic ground state reaction is allowed via either a supra/supra or antara/antara topology.
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Generalized synchronous double group transfer reaction between a component with p π electrons and a component with q π electrons.
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Conrotatory motion is antarafacial, while disrotatory motion is suprafacial.
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Illustration of the assignment of orbital overlap as suprafacial or antarafacial for common pericyclic components.
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A thermally-allowed supra-antara [2+2]-dimerization of a strained trans-olefin
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The Diels-Alder reaction is suprafacial with respect to both components.
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Berson's classic (1967) example of a [1,3]-sigmatropic alkyl shift proceeding with stereochemical inversion (WH symbol [σ2a + π2s])
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Hypothetical Huckel versus Mobius aromaticity.
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Dual-descriptor coloring (red>0, blue
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Anti-WH product via disrotatory mechanism induced by ring strain.
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See also
In Spanish: Reglas de Woodward-Hoffmann para niños
