A @C01234@ 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 \(\rightarrow \) enol prototropy of pentane-2,4-dione (acetylacetone).
Because the \(\pi \)- and \(\sigma \)-atomic orbitals that interchange roles are orthogonal, such a reaction does not proceed through a fully @C01267@ and is thus not a @P04491@ and therefore not governed by the rules that express @O04320@ restrictions applicable to pericyclic reactions.
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1154 [Terms] [Paper]