Warning (2): get_headers(): https:// wrapper is disabled in the server configuration by allow_url_fopen=0 [APP/Controller/TermsController.php, line 315]
Warning (2): get_headers() [<a href='http://php.net/function.get-headers'>function.get-headers</a>]: This function may only be used against URLs [APP/Controller/TermsController.php, line 315]

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 superposable 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 polytopal rearrangement that provides an intramolecular mechanism for the isomerization of trigonal bipyramidal compounds (e.g. λ5-phosphanes), the five bonds to the central atom E being represented as e1, e2, e3, a1 and a2. Two equatorial bonds move apart and become apical bonds at the same time as the apical bonds move together to become equatorial.
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 equatorial 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 (https://doi.org/10.1351/pac199668122193)