Outline of Contents

  1. Introduction to Pericyclic Reactions
    Reaction classes:  Polar v. concerted
    Covalent bonding
    Frontier molecular orbitals (FMOs)
  2. The [4π + 2π] Cycloaddition (Diels-Alder Reaction)
    FMO interactions
    Stereoselectivity and regioselectivity
    Substituent effects and Lewis acid catalysis
  3. Other Concerted [n + m] Cycloadditions
    [2 + 2] Processes ('forbidden' and 'allowed' variants)
    Other (4n + 2) and (4n) pairings
    Selection rules
  4. Selection Rules and Orbital Symmetry
    Cycloadditions exemplified
    Introduction to electrocyclic reactions
    Conservation of orbital symmetry in the ring-opening of cyclobutene
  5. Electrocyclic Reactions
    Valence tautomerisation processes
  6. 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

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