Advanced Topic 843 of 1102 Organic Chemistry
Pericyclic Reactions
Concerted reactions through cyclic transition states governed by orbital symmetry.
In-depth explanation of Pericyclic Reactions
Pericyclic reactions are concerted reactions that proceed through a cyclic arrangement of orbitals, with all bond changes occurring in one step. The main types are cycloadditions, electrocyclic reactions and sigmatropic rearrangements, and they are not influenced by polar solvents or catalysts in the usual way. Their stereochemistry and feasibility are governed by the symmetry of the molecular orbitals involved, and the thermal and photochemical conditions can give different products. These reactions are often stereospecific and produce predictable products.
Going deeper: Pericyclic Reactions
Key ideas: Concerted reactions through a cyclic transition state without intermediates: cycloadditions (Diels-Alder), electrocyclic ring opening or closing, sigmatropic shifts (Cope, Claisen) and ene reactions. Unaffected by radical initiators or polar solvents, but controlled by light or heat via orbital symmetry. Classification uses the number of electrons and whether they react suprafacially or antarafacially.
Common mistakes and connections: Students look for charged intermediates that are not there. Another error is thinking thermal and photochemical reactions give the same stereochemical outcomes; they are opposite. Links to Woodward-Hoffmann rules, frontier orbital theory and aromatic transition states.
Visualization of Pericyclic Reactions
Pericyclic reactions proceed through a cyclic arrangement of overlapping p orbitals in one concerted step, as seen in the shape of a 2p lobe. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The Cope rearrangement of 1,5-hexadiene is a sigmatropic shift in which a sigma bond moves through a six-membered cyclic transition state.
Frequently asked questions about Pericyclic Reactions
What is Pericyclic Reactions?
Concerted reactions through cyclic transition states governed by orbital symmetry.
Is Pericyclic Reactions a beginner, intermediate or advanced topic?
Pericyclic Reactions is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Pericyclic Reactions?
Study these earlier topics in Organic Chemistry first: Wittig Reaction, Claisen Condensation, Michael Addition.
What comes after Pericyclic Reactions?
The next topics in Organic Chemistry are Woodward-Hoffmann Rules and Cross-Coupling Reactions.
Can I practise Pericyclic Reactions with quizzes?
Yes. The interactive lesson includes a self-check question on Pericyclic Reactions, and the Organic Chemistry quiz draws on every topic in this area.
Where Pericyclic Reactions fits in Organic Chemistry
Pericyclic Reactions is topic 115 of 148 in Organic Chemistry.