## Wikipedia - Pseudorotation pseudorotation

Also contains definitions of: Berry pseudorotation, turnstile rotation
https://doi.org/10.1351/goldbook.P04934
Stereoisomerization resulting in a structure that appears to have been produced by rotation of the entire initial molecule and is @S06144@ on the initial one, unless different positions are distinguished by substitution, including isotopic substitution. One example of pseudorotation is a facile interconversion between the many envelope and twist conformers of a cyclopentane due to the out of plane motion of carbon atoms. Another example of pseudorotation (Berry pseudorotation) is a @P04755@ that provides an @I03130@ mechanism for the @I03295@ of trigonal bipyramidal compounds (e.g. $$\lambda ^{5}$$-@P04548@), the five bonds to the @C00930@ E being represented as $$\text{e}^{1}$$, $$\text{e}^{2}$$, $$\text{e}^{3}$$, $$\text{a}^{1}$$ and $$\text{a}^{2}$$. Two @A00415-1@ bonds move apart and become @A00415-2@ bonds at the same time as the apical bonds move together to become @E02174@.
P04934-1.png
A related conformational change of a trigonal bipyramidal structure is described as turnstile rotation. The process may be visualized as follows.
P04934-2.png
An apical and an @E02174@ bond rotate as a pair ca. 120° relative to the other three bonds. (Doubts have been expressed about the distinct physical reality of this mechanism.)
Source:
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2215 [Terms] [Paper]