What does pericyclic mean?
Pericyclic is an adjective used in organic chemistry for reactions that occur through a cyclic transition state. During a pericyclic reaction, bonds break and new bonds form in a coordinated, concerted sequence rather than through separate, isolable ionic or radical intermediates. The participating atoms or orbitals form a cyclic arrangement at the key stage of the reaction, and orbital-symmetry principles can determine whether the process is allowed. Familiar examples include the Diels–Alder reaction, the ene reaction, and certain sigmatropic rearrangements. The term is useful because it identifies a shared mechanistic pattern across reactions that can otherwise look very different. It is primarily encountered in university-level chemistry, professional research, and advanced educational material rather than in general conversation.
adjectiveOf or relating to a chemical reaction in which bonds break and reform simultaneously through a cyclic transition state. Such reactions are concerted processes involving a cyclic arrangement of interacting molecular orbitals.
- Relating to a chemical reaction involving a cyclic transition state and simultaneous bond breaking and bond formation.
"The Diels–Alder reaction is a classic example of a pericyclic cycloaddition."
"The reaction proceeded through a pericyclic transition state in which all the relevant bonds changed at once."
"Chemists used orbital-symmetry rules to predict whether the proposed pericyclic reaction would be allowed."
Pericyclic reactions turn the movement of electrons into a carefully choreographed cycle, producing dramatic molecular rearrangements without a traditional ionic intermediate.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does pericyclic come from?
The word combines the prefix peri-, meaning around, with cyclic, relating to a cycle. This reflects the defining feature of these reactions: the atoms and electrons involved pass through a cyclic arrangement during the transition state. The related forms cycle, cyclic, bicycle, and tricycle all derive from the Greek root kyklos, meaning circle or wheel.
Related word forms
How pericyclic is actually used
This is a specialist chemistry term. It is normally used with words such as “reaction,” “transition state,” and “cycloaddition,” and is not ordinarily applied to unrelated processes involving circles.