Outline of Contents
- Introduction to Pericyclic Reactions
Reaction classes: Polar v. concerted
Covalent bonding
Frontier molecular orbitals (FMOs) - The [4π + 2π] Cycloaddition (Diels-Alder Reaction)
FMO interactions
Stereoselectivity and regioselectivity
Substituent effects and Lewis acid catalysis - Other Concerted [n + m] Cycloadditions
[2 + 2] Processes ('forbidden' and 'allowed' variants)
Other (4n + 2) and (4n) pairings
Selection rules - Selection Rules and Orbital Symmetry
Cycloadditions exemplified
Introduction to electrocyclic reactions
Conservation of orbital symmetry in the ring-opening of cyclobutene - Electrocyclic Reactions
Hexatriene-cyclohexadiene
Cyclopropyl-allyl
Valence tautomerisation processes - Sigmatropic Rearrangements
[1,5] and [1,7] Hydrogen shifts
[1,3] Sigmatropic shifts
[3,3] Sigmatropic rearrangements
Cope and Claisen rearrangements
Recommended Texts and Support
- J. Clayden, N. Greeves, S. Warren and P. Wothers, Organic Chemistry (Oxford University Press, 2001) ISBN 0198503466 (Ch. 35, 36).
- J. Clayden, N. Greeves and S. Warren, Organic Chemistry 2nd edition (Oxford University Press, 2012) ISBN 0199270295 (Ch. 34, 35).
- I. Fleming, Pericyclic Reactions (Oxford Chemistry Primer, no. 67, 2nd edition) (Oxford University Press, 2015) ISBN 0199680900 (affordable, thorough guidebook).
- I. Fleming, Molecular Orbitals and Organic Chemical Reactions: Student Edition (Wiley-Blackwell, 2009) ISBN 0470746599 (comprehensive reference text).
- The Conservation of Orbital Symmetry: R. B. Woodward and R. Hoffmann, Angew. Chem., Int. Ed. 1969, 8, 781–853.
DOI: 10.1002/anie.196907811 - A set of molecular models (e.g. Orbit by Cochranes of Oxford) is invaluable.
Background and Acknowledgements
The original version of this website was designed to support a Core Organic Chemistry unit on reaction intermediates and mechanisms, for the use of MChem students in the School of Chemistry of the University of Manchester. Representative pericyclic processes — cycloadditions, electrocyclic reactions and sigmatropic rearrangements — are analysed using frontier molecular orbital (FMO) methods. For illustrative examples, the molecular orbitals of key structures were calculated using Spartan 08 (Hartree-Fock, 6-31G* basis set, unless otherwise indicated) and can be visualised in the form of interactive 3-D models generated with JSmol, an open-source JavaScript-based molecular viewer. The website was revamped during 2017-18 with the aim of improving its 'device compatibility' and visual quality. I extend my thanks and appreciation to Garry Procter, Ian Fleming and Angel Herráez for their various contributions to the original project, and to Stuart Anderson for providing the template on which the updated website is based.
Tim Wallace
Manchester, July 2018