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 @[email protected] 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 @[email protected] that provides an @[email protected] mechanism for the @[email protected] of trigonal bipyramidal compounds (e.g. \(\lambda ^{5}\)[email protected]@), the five bonds to the @[email protected] E being represented as \(\text{e}^{1}\), \(\text{e}^{2}\), \(\text{e}^{3}\), \(\text{a}^{1}\) and \(\text{a}^{2}\). Two @[email protected] bonds move apart and become @[email protected] bonds at the same time as the apical bonds move together to become @[email protected]
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 @[email protected] 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]