Term: pseudopericyclic
https://doi.org/10.1351/goldbook.P04932

Definition:
A concerted transformation is pseudopericyclic if the primary changes in bonding occur within a cyclic array of atoms at one (or more) of which nonbonding and bonding atomic orbitals interchange roles. A formal example is the enol → enol prototropy of pentane-2,4-dione (acetylacetone). P04932.png Because the π- and σ-atomic orbitals that interchange roles are orthogonal, such a reaction does not proceed through a fully conjugated transition state and is thus not a pericyclic reaction and therefore not governed by the rules that express orbital symmetry restrictions applicable to pericyclic reactions.

Related Terms:
1) concerted transformation (http://doi.org/10.1351/goldbook.C01234).
2) conjugated transition state (http://doi.org/10.1351/goldbook.C01267).
3) orbital symmetry (http://doi.org/10.1351/goldbook.O04320).
4) pericyclic reaction (http://doi.org/10.1351/goldbook.P04491).

Image: Not defined (https://goldbook.iupac.org/img/inline/P04932.png) 

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1154 (https://doi.org/10.1351/pac199466051077)

Citation: 'pseudopericyclic' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.P04932

License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.

Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.