Also contains definitions of: Berry pseudorotation, turnstile rotation
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]
A related conformational change of a trigonal bipyramidal structure is described as turnstile rotation. The process may be visualized as follows.
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.)
PAC, 1996, 68, 2193. (Basic terminology of stereochemistry (IUPAC Recommendations 1996)) on page 2215 [Terms] [Paper]